Control of supercharger

ABSTRACT

An engine is provided with a turbocharger which varies a supercharging pressure by an actuator. A controller calculates a first compensation value of a response delay from operation of the actuator to variation of an intake air amount of the engine, and a second compensation value of an operating delay of the actuator with respect to an input of a command signal to the actuator. The command signal to the actuator is calculated by performing a processing based on the first compensation and the second compensation value on an operational target value that was determined based on the running state of the engine, and the response of intake air amount control is thereby enhanced.

FIELD OF THE INVENTION

This invention relates to control of an intake fresh air amount of anengine provided with a turbocharger.

BACKGROUND OF THE INVENTION

Tokkai Hei 11-132049 published by the Japanese Patent Office in 1999discloses a method of processing a command signal for enhancing theresponse characteristics of the supercharging pressure control of aturbocharger of an engine. The turbocharger is provided with an exhaustgas turbine driven by the exhaust gas of the engine, and a compressorwhich rotates together with the exhaust gas turbine to supercharge theintake air of the engine. The turbocharger is further provided with avariable nozzle that regulates the inflow cross-sectional area ofexhaust gas to the exhaust gas turbine.

The inflow cross-sectional area of exhaust gas varies according to theopening of the variable nozzle that is varied by an actuator.

This prior art technique discloses an idea that the intake air amount ofthe engine varies with a first order delay with respect to the commandsignal input to the actuator, and proposes to apply an advanceprocessing to the command signal for cancelling out the first orderdelay in order to enhance the precision of control of the intake airamount of the engine.

SUMMARY OF THE INVENTION

There are the following problems in taking the delay from the variationof the command signal to the actuator, until the intake air amount of anengine changes, to be a simple first order delay.

Various kinds of delay may be anticipated between the command signalinput to the actuator and the variation of the intake air amount of theengine, such as a delay depending on the flow velocity of intake air andexhaust gas, a turbo lag due to the construction of the gasturbine/compressor, and a delay in the operation of the actuator itself.

These lags do not necessarily vary with the same parameters.

For example, a time constant of the lag depending on the flow velocityof the intake air and exhaust gas and a time constant of the turbo lag,vary depending on the exhaust gas amount of the engine. On the otherhand, a time constant of the operating delay of the actuator is fixedregardless of the exhaust gas amount.

Therefore, it is difficult to enhance the precision of controlling theintake air amount by simply applying an advance processing based on afirst order delay to the command signal to the actuator.

It is therefore an object of this invention to perform delaycompensation in the control of a turbocharger with higher precision.

In order to achieve the above object, this invention provides a controldevice for a turbocharger of an engine, wherein the turbocharger isprovided with an actuator which adjusts an intake air amount of theengine according to a command signal. The control device comprises asensor which detects a running state of the engine, and a controllerfunctioning to set a target intake air amount of the engine based on therunning state, calculate an operational target value of the actuatorbased on the target intake air amount, calculate a first compensationvalue of a response delay from operation of the actuator to variation ofthe intake air amount, calculate a second compensation value of anoperating delay of the actuator with respect to an input of the commandsignal to the actuator, calculate the command signal by performing aprocessing based on the first compensation value and the secondcompensation value on the operational target value, and output thecommand signal to the actuator.

This invention also provides a control method of a turbocharger of anengine, wherein the turbocharger is provided with an actuator whichadjusts an intake air amount of the engine according to a commandsignal. The control method comprising detecting a running state of theengine, setting a target intake air amount of the engine based on therunning state, calculating an operational target value of the actuatorbased on the target intake air amount, calculating a first compensationvalue of a response delay from operation of the actuator to variation ofthe intake air amount, calculating a second compensation value of anoperating delay of the actuator with respect to an input of the commandsignal to the actuator, calculating the command signal by performing aprocessing based on the first compensation value and the secondcompensation value on the operational target value, and outputting thecommand signal to the actuator.

The details as well as other features and advantages of this inventionare set forth in the remainder of the specification and are shown in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a control device for a diesel engineaccording to this invention.

FIG. 2 is a schematic diagram of a common rail fuel injection mechanismwith which the diesel engine is provided.

FIG. 3 is a flowchart describing a routine for calculating a target fuelinjection amount Qsolperformed by a controller according to thisinvention.

FIG. 4 is a diagram describing the contents of a map of a basic fuelinjection amount Mqdrv stored by the controller.

FIG. 5 is a diagram describing the contents of a map of an EGR valvelift amount stored by the controller.

FIG. 6 is a flowchart describing a routine for calculating a target EGRamount Tqec per cylinder performed by the controller.

FIG. 7 is a flowchart describing a routine for calculating a cylinderintake fresh air amount Qac performed by the controller.

FIG. 8 is a flowchart describing a routine for calculating an intakefresh air flowrate Qas0 of the intake passage performed by thecontroller.

FIG. 9 is a diagram describing the contents of an intake fresh airamount map stored by the controller.

FIG. 10 is a flowchart describing a routine for calculating a target EGRrate Megr performed by the controller.

FIG. 11 is a diagram describing the contents of a map of a basic targetEGR rate Megrb stored by the controller.

FIG. 12 is a diagram describing the contents of a map of a watertemperature correction coefficient Kegr_tw stored by the controller.

FIG. 13 is a flowchart describing a complete combustion determiningroutine performed by the controller.

FIG. 14 is a flowchart describing a routine for calculating an EGR rateMegrd in an intake valve position performed by the controller.

FIG. 15 is a flowchart describing a routine for calculating a timeconstant inverse value Kkin performed by the controller.

FIG. 16 is a flowchart describing the contents of a map of a volumeefficiency equivalent basic value Kinb performed by the controller.

FIG. 17 is a flowchart describing a routine for calculating a targetintake fresh air amount tQac performed by the controller.

FIG. 18 is a diagram describing the contents of a map of a target intakefresh air amount basic value tQacb stored by the controller.

FIG. 19 is a diagram describing the contents of a map of a correctioncoefficient ktQac stored by the controller.

FIG. 20 is a diagram describing the contents of a map of a target intakefresh air amount tQac stored by the controller.

FIG. 21 is a flowchart describing a routine for calculating a real EGRamount Qec performed by the controller.

FIG. 22 is a flowchart describing a subroutine for calculating an EGRamount feedback correction coefficients Kqac00, an EGR flow velocityfeedback correction coefficient Kqac0, and an EGR flow velocity learningcorrection coefficient Kqac, performed by the controller.

FIG. 23 is a flowchart describing a routine for setting a feedbackcontrol permission flag fefb performed by the controller.

FIG. 24 is a flowchart describing a routine for setting a learning valuereflection permission flag felrn2 performed by the controller.

FIG. 25 is a flowchart describing a routine for setting a learningpermission flag felrn performed by the controller.

FIG. 26 is a flowchart describing a subroutine for calculating the EGRamount feedback correction coefficient Kqac00 performed by thecontroller.

FIG. 27 is a diagram describing the contents of a map of a correctiongain Gkfb of an EGR flowrate stored by the controller.

FIG. 28 is a diagram describing the contents of a map of a watertemperature correction coefficient Kgfbtw of an EGR amount stored by thecontroller.

FIG. 29 is a flowchart describing a subroutine for calculating the EGRflow velocity feedback correction coefficient Kqac0 performed by thecontroller.

FIG. 30 is a diagram describing the contents of a map of an EGR valveflow velocity correction gain Gkfbi stored by the controller.

FIG. 31 is a diagram describing the contents of a map of a watertemperature correction coefficient Kgfbitw of an EGR flow velocitystored by the controller.

FIG. 32 is a diagram describing the contents of a map of an error ratelearning value Rqac_(n) stored by the controller.

FIG. 33 is a flowchart describing a subroutine for updating the errorrate learning value Rqac_(n) performed by-the controller.

FIG. 34 is a diagram describing the contents of a map of a learning rateTclrn stored by the controller.

FIG. 35 is a flowchart describing a routine for calculating an EGR valveflow velocity Cqe performed by the controller.

FIG. 36 is a diagram describing the contents of a map of the EGR valveflow velocity Cqe stored by the controller.

FIG. 37 is a flowchart describing a routine for calculating a targetopening area Aev of the EGR valve performed by the controller.

FIG. 38 is a flowchart describing a routine for setting a duty valueDtyvnt of a pressure control valve of a variable nozzle performed by thecontroller.

FIG. 39 is a flowchart describing a subroutine for setting an overboostdetermining flag FOVBST performed by the controller.

FIGS. 40A-40E are timing charts describing a variation of the overboostdetermining flag FOVBST with respect to a variation of an acceleratoropening.

FIG. 41 is a diagram describing the contents of a map of an overboostdetermining intake gas amount TQcyl stored by the controller.

FIG. 42 is a diagram describing the characteristics of an efficiency ofa turbocharger with which the diesel engine is provides.

FIG. 43 is a flowchart describing a subroutine for setting a suppressionrelease flag FCLROB performed by the controller.

FIGS. 44A and 44B are timing charts describing a variation of theoverboost determining flag FOVBST and the suppression release flagFCLROB.

FIG. 45 is a flowchart describing a routine for calculating an overboostsuppressing period TTMROB performed by the controller.

FIG. 46 is a diagram describing the contents of a map of an overboostsuppressing period basic value TTMROB0 stored by the controller.

FIG. 47 is a diagram describing the contents of a map of an overboostsuppressing period correction coefficient KTMROB stored by thecontroller.

FIG. 48 is a flowchart describing a routine for calculating asuppression release period TTMRCLROB performed by the controller.

FIG. 49 is a diagram describing the contents of a map of a suppressionrelease period basic value TTMRCLROB0 stored by the controller.

FIG. 50 is a diagram describing the contents of a map of a suppressionrelease period correction coefficient KTMRCLROB stored by thecontroller.

FIG. 51 is a flowchart describing a subroutine for calculating a targetopening rate Rvnt of the variable nozzle performed by the controller.

FIG. 52 is a diagram describing the contents of a map of a targetopening rate basic value Rvnt0 of the variable nozzle in an EGRoperation region under the overboost suppressing control, stored by thecontroller.

FIG. 53 is a diagram describing the contents of a map of the targetopening rate basic value Rvnt0 of the variable nozzle in the EGRoperation region under a normal engine control, stored by thecontroller.

FIG. 54 is a diagram describing the contents of a map of a targetopening rate basic value Rvnt0 of the variable nozzle in a non-EGRoperation region under the overboost suppressing control, stored by thecontroller.

FIG. 55 is a diagram describing the contents of a map of a targetopening rate basic value Rvnt0 of the variable nozzle in the non-EGRoperation region under the normal engine control, stored by thecontroller.

FIG. 56 is similar to FIG. 51, but showing a second embodiment of thisinvention with respect to the subroutine for calculating the targetopening rate Rvnt of the variable nozzle.

FIG. 57 is a diagram describing the contents of a map of the targetopening rate basic value Rvnt0 of the variable nozzle in the EGRoperation region under the overboost suppressing control, according tothe second embodiment of this invention.

FIG. 58 is a diagram describing the contents of a map of the targetopening rate basic value Rvnt0 of the variable nozzle in the EGRoperation region under the normal engine control, according to thesecond embodiment of this invention.

FIGS. 59A-59C are timing charts describing an effect of an EGR rate onan exhaust gas composition and an intake fresh air amount of the dieselengine.

FIG. 60 is a flowchart describing a routine for calculating an open loopcontrol amount Avnt_f of an opening rate of the variable nozzle and adelay processing value Rvnte of the target opening rate Rvnt of thevariable nozzle performed by the controller.

FIGS. 61A-61D are timing charts describing a variation of an exhaust gasamount of the diesel engine with respect to a variation of a fuelinjection amount.

FIG. 62 is a diagram describing the contents of a map of an advancecorrection gain TGKVNTO when the variable nozzle is operating in anopening direction, stored by the controller.

FIG. 63 is a diagram describing the contents of a map of an advancecorrection gain TGKVNTC when the variable nozzle is operating in aclosing direction, stored by the controller.

FIG. 64 is a diagram describing the contents of a map of a time constantinverse value TTCVNTO of an advance correction of the opening rate ofthe variable nozzle when it is operating in the opening direction,stored by the controller.

FIG. 65 is a diagram describing the contents of a map of a time constantinverse value TTCVNTC of the advance correction of the opening rate ofthe variable nozzle when it is operating in the closing direction,stored by the controller.

FIG. 66 is a flowchart describing a subroutine for calculating afeedback correction amount Avnt_fb of the opening rate of the variablenozzle and an opening rate learning value Ravlr performed by thecontroller.

FIG. 67 is a flowchart describing a subroutine for setting a feedbackcontrol permission flag FVNFB of the opening rate of the variable nozzleperformed by the controller.

FIG. 68 is a diagram showing an operation region of the diesel enginewhere the controller feedback controls the opening rate of the variablenozzle.

FIG. 69 is a flowchart describing a subroutine for setting feedbackgains of the opening rate of the variable nozzle.

FIG. 70 is a diagram describing the contents of a map of a proportionalgain basic value Gkvntp0 stored by the controller.

FIG. 71 is a diagram describing the contents of a map of an integralgain basic value Gkvnti0 stored by the controller.

FIG. 72 is a diagram describing the contents of a map of an exhaust gasamount correction coefficient Gkvqexh stored by the controller.

FIG. 73 is a diagram describing the contents of a map of an opening ratecorrection coefficient Gkvavnt stored by the controller.

FIG. 74 is a flowchart describing a subroutine for calculating thefeedback correction amount Avnt_fb of the opening rate of the variablenozzle performed by the controller.

FIG. 75 is a flowchart describing a subroutine for setting a learningpermission flag FVNLR of the opening rate of the variable nozzleperformed by the controller.

FIG. 76 is a diagram showing an operation region of the diesel enginewhere the controller perform learning control of the opening rate of thevariable nozzle.

FIG. 77 is a flowchart describing a subroutine for calculating theopening rate learning value Ravlr performed by the controller.

FIG. 78 is a diagram describing the contents of a map of a learningspeed Kvntlrn stored by the controller.

FIG. 79 is a diagram describing the contents of a map of an operationregion reflection coefficient Gkvntlnq stored by the controller.

FIG. 80 is a diagram describing the contents of a map of an opening ratereflection coefficient Gkvntlav stored by the controller.

FIG. 81 is a flowchart describing a subroutine for calculating a commandopening rate linearization processing value Ratdty performed by thecontroller.

FIG. 82 is a flowchart describing a subroutine for calculating a finalcommand opening rate Trvnt performed by the controller.

FIG. 83 is a diagram describing the contents of a map of the commandopening rate linearization processing value Ratdty stored by thecontroller.

FIG. 84 is a flowchart describing a subroutine for calculating a commandduty value Dtyv output to the pressure control valve, performed by thecontroller.

FIG. 85 is a flowchart describing a subroutine for setting a duty holdflag fvnt2 performed by the controller.

FIG. 86 is a flowchart describing a subroutine for calculating atemperature correction amount Dty_t performed by the controller.

FIG. 87 is a diagram describing the contents of a map of a basic exhaustgas temperature Texhb stored by the controller.

FIG. 88 is a diagram describing the contents of a map of a watertemperature correction coefficient Ktexh_Tw stored by the controller.

FIG. 89 is a diagram describing the contents of a map of the temperaturecorrection amount Dty_t stored by the controller.

FIG. 90 is a diagram describing an effect of the temperature on therelation between the duty value of the pressure control valve and theopening rate of the variable nozzle.

FIG. 91 is a diagram of the contents of a map of a duty value Duty_f_pwhen the variable nozzle is fully closed while the command opening ratelinearization processing value Ratdty is increasing, stored by thecontroller.

FIG. 92 is a diagram of the contents of a map of a duty value Duty_l_pwhen the variable nozzle is fully open while the command opening ratelinearization processing value Ratdty is increasing, stored by thecontroller.

FIG. 93 is a diagram of the contents of a map of a duty value Duty_h_nwhen the variable nozzle is fully closed while the command opening ratelinearization processing value Ratdty is decreasing, stored by thecontroller.

FIG. 94 is a diagram of the contents of a map of a duty value Duty_l_nwhen the variable nozzle is fully open while the command opening ratelinearization processing value Ratdty is decreasing, stored by thecontroller.

FIG. 95 is a diagram describing a hysteresis in the relation between thecommand opening rate linearization processing value Ratdty and the dutyvalues according to this invention.

FIG. 96 is a flowchart describing a subroutine for checking theoperation of the variable nozzle performed by the controller.

FIG. 97 is a flowchart describing a routine for calculating the dutyvalue Dtyvnt of the pressure control valve performed by the controller.

FIG. 98 is a diagram describing the contents of a map of a controlpattern value Duty_pu stored by the controller.

FIG. 99 is a diagram describing the contents of a map of a duty valueDuty_p_ne for checking the operation of the variable nozzle, stored bythe controller.

FIG. 100 is a diagram showing the relation between a charging efficiencyof a turbocharger, a corrected mass flowrate QA and a pressure ratio π.

FIG. 101 is a diagram showing the relation between the chargingefficiency, an exhaust gas amount of a diesel engine and an EGR amountthereof.

FIG. 102 is a timing chart showing simulation results when an advancecorrection is applied to the opening rate of a variable nozzle, settinga time constant equivalent value Tcvnt to 0.1 and an advance correctiongain Gkvnt to 2.

FIG. 103 is similar to FIG. 102, but showing a simulation result whenthe advance correction gain Gkvnt is set to 0.5.

FIGS. 104A-104E is a timing chart showing a variation of the targetopening rate Rvnt and a cylinder intake fresh air amount Qac in a smallexhaust gas amount region, in the control device according to thisinvention.

FIGS. 105A-105E are similar to FIGS. 104A-104E, but showing a variationof the target opening rate Rvnt and the cylinder intake fresh air amountQac in a large exhaust gas amount region.

FIG. 106 is a flowchart describing a routine for calculating an EGRvalve opening surface area Aev performed by a controller according to athird embodiment of this invention.

FIG. 107 is a diagram showing the contents of a map of a target EGRvalve opening surface area Eaev per unit exhaust gas amount stored bythe controller according to the third embodiment of this invention.

FIG. 108 is similar to FIG. 107, but showing a theoretical value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a diesel engine 1 comprises anintake passage 3 and exhaust passage 2. The diesel engine 1 is amulti-cylinder diesel engine so constructed that the pattern of heatrelease is single stage combustion due to performing low temperaturepre-mixture combustion. Such a diesel engine is disclosed by Tokkai Hei8-86251 published by the Japanese Patent Office in 1999. Intake air ofthe intake air passage 3 is supplied to each cylinder of the dieselengine 1 via a collector 3A.

A compressor 55 of a turbocharger 50 and a intake throttle 60 driven bya throttle actuator 61 are installed in the intake passage 3 upstream ofthe collector 3A.

A swirl control valve is provided in an intake port leading from theintake passage 3 to each cylinder. When the diesel engine 1 is runningat low rotation speed on low load, the swirl control valve closes partof the passage and sets up a swirl in the flow of air flowing into thecombustion chamber of the diesel engine 1.

The combustion chamber comprises a large diameter toroidal combustionchamber. This is a combustion chamber wherein a cylindrical cavity ofthe same diameter is formed on a piston from a cap surface to a base. Aconical part is formed at the base of the cavity. As a result,resistance to the swirl flowing in from the outside of the cavity isreduced, and mixing of air and fuel is promoted. Also, due to the shapeof the cavity, the swirl diffuses from the center of the cavity to theoutside as the piston descends.

The diesel engine 1 comprises a common rail type fuel injectionmechanism 10.

Referring to FIG. 2, a fuel injection mechanism 10 comprises a fuel tank11, fuel supply passage 12, supply pump 14, pressure accumulatingchamber 16A formed in a common rail 16, and a nozzle 17 which isprovided for every cylinder. After the fuel supplied from the supplypump 14 is stored in a pressure accumulator 16A via a high pressure fuelpassage 15, it is distributed to each of the nozzles 17.

The nozzle 17 comprises a needle valve 18, nozzle chamber 19, fuelpassage 20 to the nozzle chamber 19, retainer 21, hydraulic piston 22,return spring 23, fuel passage 24 which leads high pressure fuel to thehydraulic piston 22, and three-way solenoid valve 25 interposed in thefuel passage 24. A check valve 26 and an orifice 27 are also provided inparallel in the fuel passage 24. The return spring 23 pushes the needlevalve 18 in the closing direction of the lower part of the figure viathe retainer 21. The hydraulic piston 22 comes in contact with the upperedge of the retainer 21.

The three-way valve 25 comprises a port A connected to the pressureaccumulating chamber 16A, port B connected to the fuel passage 24 andport C connected to a drain 28. When the three-way valve 25 is OFF,ports A and B are connected and ports B and C are shut off. As a result,the fuel passages 20 and 24 are connected, and high pressure fuel is ledto both the upper part of the hydraulic piston 22 and the nozzle chamber19 from the pressure accumulating chamber 16A. As the pressure-receivingsurface area of the hydraulic piston 22 is larger than thepressure-receiving surface area of the needle valve 18, in this state,the needle valve 18 sits in the valve seat, and the nozzle 17 is therebyclosed.

In the state where the three-way valve 25 is ON, the ports A and B areshut off, and the ports B and C are connected.

Consequently, the fuel pressure of the fuel passage 24 which pushes thehydraulic piston 22 downward is released to the fuel tank 11 via thedrain 28, the needle valve 18 lifts due to the fuel pressure of thenozzle chamber 19 which acts on the needle valve 18 in an upwarddirection, and the fuel of the nozzle chamber 19 is injected from thehole at the end of the nozzle 17. If the three-way valve 25 is returnedto the OFF state, the fuel pressure of the pressure accumulating chamber16A again acts downward on the hydraulic piston 22, the needle valve 18sits in the valve seat, and fuel injection is terminated.

That is, fuel injection start timing is adjusted by the change-overtiming from OFF to ON of the three-way valve 25, and fuel injectionamount is adjusted by the duration of the ON state. Therefore, if thepressure of the pressure accumulating chamber 16A is the same, the fuelinjection amount increases the longer the ON time of the three-way valve25.

Further, to adjust the pressure of the pressure accumulating chamber16A, the fuel injection mechanism 10 comprises a return passage 13 whichreturns the surplus fuel discharged by the supply pump 14 to the fuelsupply passage 12. The return passage 13 is provided with a pressureregulating valve 31. The pressure regulating valve 31 opens and closesthe return passage 13, and adjusts the pressure of the pressureaccumulating chamber 16A by varying the fuel injection amount to thepressure accumulating chamber 16A.

The fuel pressure of the pressure accumulating chamber 16A is equal tothe fuel injection pressure of the nozzle 17, and the fuel injectionrate is higher the higher the fuel pressure of the pressure accumulatingchamber 16. The three-way valve 25 and the pressure regulating valve 31function according to the input signal from a controller 41.

The above construction of the fuel injection mechanism 10 is disclosedand known from pp. 73-77, Lecture Papers of the 13th Symposium on theInternal Combustion Engine.

Now, referring again to FIG. 1, after the exhaust gas in the exhaustpassage 2 drives an exhaust gas turbine 52 of the turbocharger 50, it isdischarged into the atmosphere via a catalytic converter 62. Thecatalytic converter 62 traps nitrogen oxides (NOx) when the dieselengine 1 operates under a lean air-fuel ratio, and reduces the trappedNOx by hydrocarbon (HC) contained in the exhaust gas when the dieselengine 1 operates under a rich air-fuel ratio.

The turbocharger 50 comprises the exhaust gas turbine 52 and thecompressor 55 which supercharges the intake fresh air in the intakepassage 3 according to the rotation of the exhaust gas turbine 52. Thecompressor 55 is provided in the middle of the intake passage 3, and theintake passage 3 supplies air compressed by the compressor 55 to thediesel engine 1. A variable nozzle 53 driven by a pressure actuator 54is provided at an inlet to the exhaust gas turbine 52.

The pressure actuator 54 comprises a diaphragm actuator 59 which drivesthe variable nozzle 53 according to a signal pressure, and a pressurecontrol valve 56 which generates the signal pressure according to asignal input from the controller 41.

The controller 41 controls the variable nozzle 53 to reduce the nozzleopening when the rotation speed of the diesel engine 1 is low. As aresult, the flow velocity of exhaust gas introduced to the exhaust gasturbine 52 is increased so that a predetermined supercharging pressureis attained. On the other hand, the controller 41 controls the variablenozzle 53 to fully open, when the rotation speed of the diesel engine 1is high, in order to introduce exhaust gas into the exhaust gas turbine52 without resistance.

When the air-fuel mixture is burnt in the diesel engine 1, noxious NOxare formed. The NOx amount largely depends on the combustiontemperature, and the generation amount of NOx can be suppressed bymaking the combustion temperature low. This diesel engine 1 reduces theoxygen concentration in the combustion chamber by exhaust recirculation(EGR), and thereby realizes low-temperature combustion. For thispurpose, the diesel engine 1 comprises an exhaust gas recirculation(EGR) passage 4 which connects the exhaust passage 2 upstream of theexhaust gas turbine 52 and a collector 3A of the intake passage 3. TheEGR passage 4 is provided with a diaphragm type exhaust gasrecirculation (EGR) valve 6 which responds to a control negativepressure provided from a negative pressure control valve 5 and a coolingsystem 7.

The negative pressure control valve 5 generates a negative pressure inresponse to a duty signal input from the controller 41, and therebyvaries the rate of exhaust gas recirculation (EGR rate) via the EGRvalve 6.

For example, in the low rotation speed, low load range of the dieselengine 1, the EGR rate is a maximum 100 percent, and as the rotationspeed and load of the diesel engine 1 increase, the EGR rate isdecreased. On high load, since the exhaust gas temperature is high,intake air temperature will rise if a large amount of EGR is performed.If the intake air temperature rises, NOx will no longer decrease, theignition delay of injected fuel becomes shorter, and it becomesimpossible to achieve pre-mixture combustion. Therefore, the EGR rate ismade to decrease in stages as the rotation speed and load of the dieselengine 1 increase.

The cooling system 7 leads part of the engine cooling water to a waterjacket 8 surrounding the EGR passage 4, and cools the recirculatedexhaust gas in the EGR passage 4. A cooling water inlet 7A of the waterjacket 8 is provided with a flow control valve 9 which adjusts therecirculating amount of cooling water according to a signal from thecontroller 41.

A pressure regulating valve 31, the three-way valve 25, the negativepressure control valve 5, the pressure actuator 54 and the flow controlvalve 9 are respectively controlled by signals from the controller 41.The controller 41 comprises a microcomputer equipped with a centralprocessing unit (CPU), random access memory (RAM), read-only memory(ROM) and input/output interface (I/O interface). It should be notedthat the controller 41 may comprise plural microcomputers.

Signals corresponding to detection values are input to the controller 41from a pressure sensor 32 which detects a fuel pressure of the pressureaccumulating chamber 16A, an accelerator opening sensor 33 which detectsan opening Cl of a vehicle accelerator pedal, a crank angle sensor 34which detects a rotation speed Ne and crank angle of the diesel engine1, a cylinder identifying sensor 35 which identifies cylinders of thediesel engine 1, a water temperature sensor 36 which detects a coolingwater temperature Tw of the diesel engine 1, an intake air temperaturesensor 37 which detects an intake air temperature Ta of the dieselengine 1, an atmospheric pressure sensor 38 which detects an atmosphericpressure Pa and an air flow meter 39 which detects an intake fresh airflowrate of the intake passage 3 upstream of the compressor 55. Theatmospheric pressure sensor 38 and air flow meter 39 are installed inthe intake passage 3 upstream of the intake throttle 60.

Based on the rotation speed of the diesel engine 1 and acceleratoropening, the controller 41 calculates a target fuel injection amount ofthe nozzle 17 and target pressure of the pressure accumulating chamber16A. The fuel pressure of the pressure accumulating chamber 16A isfeedback controlled by opening and closing the pressure regulating valve31 so that the actual pressure of the pressure accumulating chamber 16Adetected by the pressure sensor 32 coincides with the target pressure.

The controller 41 also controls an ON time of the three-way valve 25according to the calculated target fuel injection amount, and a fuelinjection start timing in response to the running conditions of thediesel engine 1 by the change-over timing to ON of the three-way valve25. For example, when the diesel engine 1 is in a low rotation speed,low load state under a high EGR rate, the fuel injection start timing isdelayed near top dead center (TDC) of the piston so that the ignitiondelay of injected fuel is long. Due to this delay, the combustionchamber temperature at the time of ignition is lowered, and thegeneration of smoke due to the high EGR rate is suppressed by increasingthe pre-mixture combustion ratio. On the other hand, the injection starttiming is advanced as the rotation speed and load of the diesel engine 1increase. This is due to the following reason. Specifically, even if theignition delay period is constant, the ignition delay crank angleobtained by converting the ignition delay period increases in proportionto the increase in engine speed. Therefore, in order to fire theinjected fuel at a predetermined crank angle, the injection start timingneeds to be advanced at high rotation speed.

The controller 41 controls the fresh air amount and the EGR amount ofthe diesel engine 1. The fresh air amount is controlled via thesupercharging pressure of the turbocharger 50 via the variable nozzle 53and the EGR amount is controlled via the EGR valve 6.

However, the supercharging pressure and the EGR amount affect eachother, and if the EGR amount is changed, it may be necessary to changethe opening of the variable nozzle 53.

As the supercharging pressure control precision and the EGR amountcontrol precision both fall when the engine 1 is in a transient state,it becomes difficult to control these parameters which are affectingeach other.

Thus, the controller 41 computes a target intake fresh air amount tQacaccording to running conditions of the engine 1, and sets a targetopening rate Rvnt of the variable nozzle 53 of the turbocharger 50 basedon this target intake fresh air amount tQac, and an EGR amount Qec percylinder in the intake valve position of the diesel engine 1, or an EGRrate Megrd in the intake valve position of the diesel engine 1.

When a turbocharger 50 increases an intake air amount according to anacceleration of a diesel engine 1, there is an exhaust gas amount regionwhere an increase in exhaust gas amount increases charging efficiency,and an exhaust gas amount region where an increase in exhaust gas amountreduces the charging efficiency.

In the exhaust gas amount region where the increase in exhaust gasamount increases the charging efficiency, a controller 41 appliesadvance processing which corrects the gas flow lag from variation of theopening rate of the variable nozzle 53 to variation of the fresh airamount, to the target opening rate Rvnt. In the exhaust gas amountregion where the increase in exhaust gas amount reduces the chargingefficiency, the controller 41 conversely applies delay processing to thetarget opening rate Rvnt.

The controller 41 further applies different advance processing forcompensating the response delay of the pressure actuator 54 to theprocessing values obtained by this advance processing or delayprocessing.

The above control performed by the controller 41 will be described withreference to flowcharts. FIG. 3, FIG. 4 and FIGS. 7-13 are known fromTokkai Hei 10-288071 published by the Japanese Patent Office in 1998.

The routine for calculating common parameters used for control ofsupercharging pressure and the EGR amount will first be described. Thecommon parameters are a target fuel injection amount Qsol of a fuelinjection mechanism 10, a target EGR rate Megr of the EGR valve 6, atime constant inverse value Kkin, a real EGR rate Megrd, a cylinderintake fresh air amount Qac, an intake fresh air flowrate Qas0 of theintake passage, the real EGR amount Qec and the target intake fresh airamount tQac.

The time constant inverse value Kkin is a value representing an EGRcontrol delay due to a collector 3A interposed between the EGR valve 6and the intake valve of the diesel engine 1. The real EGR rate Megrdshows the EGR rate of the intake air which passes through the intakevalve of the diesel engine 1. The real EGR rate Megrd varies with afirst order delay relative to the target EGR rate Megr. The calculationof these parameters is performed independently of the superchargingpressure control routine, and the EGR amount control routine.

First, referring to FIG. 3, the routine for calculating the target fuelinjection amount Qsol will be described. This routine is performed insynchronism with a REF signal output by the crank angle sensor 34 foreach reference position of the combustion cycle of each cylinder. In thecase of a four-stroke cycle engine, the REF signal is output every 180degrees for a four cylinder engine, and every 120 degrees for a sixcylinder engine.

First, in a step S1, the engine speed Ne is read, and in a step S2, theaccelerator opening Cl is read.

In a step S3, a basic fuel injection amount Mqdrv is calculated bylooking up a map shown in FIG. 4 based on the engine rotation speed Neand the accelerator opening Cl. This map is stored beforehand in thememory of the controller 41.

In a step S4, the target fuel injection amount Qsol is calculated byadding an increase correction based on an engine cooling watertemperature Tw, etc., to the basic fuel injection amount Mqdrv.

It should be noted however that the above routine does not consider theresidual air amount in the EGR gas. So, according to this invention, theactual fuel injection amount by the fuel injection mechanism 10 is notnecessarily equal to the target fuel injection amount Qsol calculated inthe above routine, but to a final target fuel injection amount Qfindescribed later.

Next, referring to FIG. 10, a routine for calculating the target EGRrate Megr will be described. This routine is also performed insynchronism with the REF signal.

The controller 41 first reads the engine rotation speed Ne, the targetfuel injection amount Qsol and the engine cooling water temperature Twin a step S51.

In a step S52, referring to a map shown in FIG. 12, the basic target EGRrate Megrb is calculated from the engine rotation speed Ne and thetarget fuel injection amount Qsol. This map is stored beforehand in thememory of the controller 41. In this map, the basic target EGR rateMegrb is set larger in a region where the operating frequency of theengine is higher. This region corresponds to a region where both therotation speed Ne and the load are small. In this map, the load isrepresented by the target fuel injection amount Qsol. When the engineoutput is high, smoke tends to be generated, so in such a region, thebasic target EGR rate Megrb is set to have small values.

In a step S53, referring to a map shown in FIG. 13, a water temperaturecorrection coefficient Kegr_Tw of the basic target EGR rate Megrb iscalculated from the cooling water temperature Tw. This map is alsostored beforehand in the memory of the controller 41.

In a step S54, the target EGR rate Megr is calculated by the followingequation (1) from the basic target EGR rate Megrb and water temperaturecorrection coefficient Kegr_Tw.

Megr=Megrb·Kegr _(—) tw  (1)

In a step S55, a subroutine shown in FIG. 13 which determines whether ornot the diesel engine 1 is in a complete combustion state, is performed.

Describing this subroutine, firstly in a step S61, the engine rotationspeed Ne is read, and in a step S62, the engine rotation speed Ne and acomplete combustion determining slice level NRPMK corresponding to acomplete combustion rotation speed are compared.

The slice level NRPMK is set, for example, to 400 rpm. When the enginerotation speed Ne exceeds the slice level NRPMK, the routine proceeds toa step S63.

Here, a counter value Tmrkb is compared with a predetermined timeTMRKBP, and when the counter value Tmrkb is larger than thepredetermined time TMRKBP, a complete combustion flag is turned ON in astep S64, and the subroutine is terminated.

When the engine rotation speed Ne is below the slice level NRPMK in thestep S62, the subroutine proceeds to a step S66. Here, the counter valueTmrkb is cleared to zero, the complete combustion flag is turned OFF ina next step S67, and the subroutine is terminated.

When the counter value Tmrkb is below the predetermined time TMRKBP inthe step S63, the counter value Tmrkb is incremented in a step S65 andthe subroutine is terminated.

In this subroutine, even if the engine rotation speed Ne exceeds theslice level NRPMK, the complete combustion flag does not turn ONimmediately, and the complete combustion flag only changes to ON afterthis state has continued for the predetermined time TMRKBP.

Referring again to FIG. 10, after performing the subroutine of FIG. 13,the controller 41 determines the complete combustion flag in a step S56.When the complete combustion flag is ON, the routine of FIG. 10 isterminated. When the complete combustion flag is OFF, the target EGRrate Megr is reset to zero in a step S57, and the routine of FIG. 10 isterminated.

Next, referring to FIGS. 14 and 15, a routine for calculating the timeconstant inverse value Kkin and the real EGR rate Megrd will now bedescribed. The real EGR rate Megrd varies with a first order delayrelative to the target EGR rate Megr. As the calculations of the timeconstant inverse value Kkin and the real EGR rate Megrd areinter-related, they will be described together.

FIG. 15 shows a routine for calculating the time constant inverse valueKkin. This routine is performed in synchronism with the REF signal.

The controller 41 reads the engine rotation speed Ne, the target fuelinjection amount Qsol and the immediately preceding value Megrd_(n−1)(%) of the real EGR rate in a step S101. The immediately preceding valueMegrd_(n−1) is a value of Megrd calculated on the immediately precedingoccasion when the routine was performed.

In a step S102, a volume efficiency equivalent basic value Kinb iscalculated from the engine rotation speed Ne and the target fuelinjection amount Qsol by looking up a map shown in FIG. 16 previouslystored in the memory of the controller 41.

In a step S103, a volume efficiency equivalent value Kin is calculatedfrom the following equation (2). When EGR is performed, the proportionof fresh air in the intake air falls, and the volume efficiencydecreases. This reduction is reflected in the calculation of the volumeefficiency equivalent value Kin via the volume efficiency equivalentbasic value Kinb. $\begin{matrix}{{Kin} = {{Kinb} \cdot \frac{1}{1 + \frac{{Megrd}_{n - 1}}{100}}}} & (2)\end{matrix}$

In a step S104, the time constant inverse value Kkin corresponding tothe capacity of the collector 3A is calculated by multiplying the volumeefficiency equivalent value Kin by a constant KVOL.

The constant KVOL is expressed by the following equation (3).

KVOL=(VE/NC)/VM  (3)

where,

VE=displacement of diesel engine 1,

NC=number of cylinders of diesel engine 1, and

VM=capacity of passage from collector 3A to the intake valve.

FIG. 14 shows the routine for calculating the real EGR rate Megrd. Thisroutine is performed at an interval of ten milliseconds.

The controller 41 first reads the target EGR rate Megr in a step S91.

In a following step S92, the time constant inverse value Kkin is read.The routine of FIG. 15, which calculates the time constant inverse valueKkin, is performed in synchronism with the REF signal, and this routinewhich calculates the real EGR rate Megrd is performed at an interval often milliseconds. Therefore, the time constant inverse value Kkin readhere is the time constant inverse value Kkin calculated by the routineof FIG. 15 immediately before the execution of the routine of FIG. 14.Likewise, the immediately preceding value Megrd_(n−1) of the real EGRrate read by the routine of FIG. 15 is the real EGR rate calculated bythe routine of FIG. 14 just before the execution of the routine of FIG.15.

In a step S93, the real EGR rate Megrd is calculated from the followingequation (4) using the target EGR rate Megr, immediately preceding valueMegrd_(n−1), and time constant inverse value Kkin.

Megrd=Megr·Kkin·Ne·Ke2 #+Megrd _(n−1)·(1−Kkin·Ne·KE2#)  (4)

where,

KE2#=constant.

In this equation, Ne·KE2# is a value to convert the EGR rate per intakestroke of each cylinder, to an EGR rate per unit time.

Next, referring to FIG. 7, a routine for calculating the cylinder intakefresh air amount Qac will be described. This routine is performed insynchronism with the REF signal. The cylinder intake fresh air amountQac expresses the intake fresh air amount in the intake valve positionof one cylinder of the diesel engine 1. The cylinder intake fresh airamount Qac is calculated from the fresh air flowrate Qas0 of the intakepassage 3 detected by the air flow meter 39, but as the air flow meter39 is situated upstream of the compressor 55, the cylinder intake freshair amount Qac is calculated considering the time until the air whichhas passed through the air flow meter 39 is taken into the cylinder viathe collector 3A.

First, in a step S31, the controller 41 reads the engine rotation speedNe and the fresh air flowrate Qas0 of the intake passage 3.

In a step S32, the intake fresh air flowrate Qas0 is converted into anintake fresh air amount Qac0 per cylinder by the following formula (5).$\begin{matrix}{{Qac0} = {{\frac{Qas0}{Ne} \cdot {KCON}}\quad \#}} & (5)\end{matrix}$

where, KCON#=constant.

The constant KCON# is a constant for converting the intake fresh airflowrate Qas0 of the intake passage 3 into the intake fresh air amountQac0 per cylinder. In a four-cylinder engine, two cylinders perform airintake in each rotation, so the constant KCON# is 30. In a six-cylinderengine, three cylinders perform air intake in each rotation, so theconstant KCON# is 20.

A considerable time is required until the air which has passed throughthe air flow meter 39 is actually taken into the cylinder. In order tocorrect for this time difference, the controller 41 performs theprocessing of steps S33, S34.

In the step S33, considering the time required from the air flow meter39 to the inlet of the collector 3A, a value Qac0 _(n−1) of Qac0 whichwas EGR flow velocity feedback correction coefficient the routineexecuted L times ago, is set as an intake fresh air amount Qacn percylinder at the inlet of the collector 3A. The value of L is determinedexperimentally.

In the step S34, considering the time difference from the collector 3Ato the intake valve of each cylinder of the diesel engine 1, thecylinder intake fresh air amount Qac is calculated by equation (6) offirst order delay.

Qac=Qac _(n−1)·(1−Kkin)+Qacn·Kkin  (6)

where,

Kkin=time constant inverse value, and

Qac_(n−1)=Qac calculated on the immediately preceding occasion theroutine was executed.

The signal input into the controller 41 from the air flow meter 39 is ananalog voltage signal Us, and the controller 41 converts the analogvoltage signal Us into the intake fresh air flowrate Qas0 of the intakepassage 3 by performing a routine shown in FIG, 8. This routine isperformed at an interval of four milliseconds.

In a step S41, the controller 41 reads the analog voltage signal Us, andin a step S42, converts this into a flowrate Qas0_d by looking up a mapshown in FIG. 9. This map is stored beforehand in the memory of thecontroller 41.

Further, in a step S43, weighted average processing is performed on theflowrate Qas0_d, and the value obtained is taken as the intake fresh airflowrate Qas0 of the intake passage 3.

Next, referring to FIG. 21, a routine for calculating the real EGRamount Qec will be described. The real EGR amount Qec corresponds to anEGR amount per cylinder in the intake valve position. This routine isperformed at an interval of ten milliseconds.

Firstly in a step S121, the controller 41 reads the intake fresh airamount Qacn per cylinder at the inlet of the collector 3A, the targetEGR rate Megr, and the time constant inverse value Kkin corresponding tothe collector capacity. For the intake fresh air amount Qacn percylinder at the inlet of the collector 3A, a value calculated by theroutine of FIG. 7 is used, and for the time constant inverse value Kkin,a value calculated by the routine of FIG. 15 is used.

In a next step S122, an EGR amount Qec0 per cylinder at the inlet of thecollector 3A is calculated by the following equation (7).

Qec 0=Qacn·Mger  (7)

In a next step S123, real EGR amount Qec is calculated by the followingequation (8) and the routine is terminated.

Qec=Qec 0·Kkin·Ne·KE#+Qec _(n−1)·(1−Kkin·Ne·KE#)  (8)

where,

Qec_(n−1)=Qec calculated on the immediately preceding occasion theroutine was performed.

The EGR amount Qec per cylinder in the intake valve position isequivalent to the real EGR amount per cylinder of the diesel engine 1.In the following description, the EGR amount Qec per cylinder in theintake valve position is referred to as the real EGR amount forsimplicity.

The real EGR amount Qec, target intake fresh air amount tQac, cylinderintake fresh air amount Qac and target EGR amount Tqek are allflowrates, but as they are usually referred to as amounts in commonusage, this will also be done in the following description.

FIG. 17 shows a routine for calculating the target intake fresh airamount tQac. This routine is performed at an interval of tenmilliseconds. The target intake fresh air amount tQac corresponds to thetarget fresh air amount at the collector 3A.

Firstly in a step S111, the control unit 41 reads the engine rotationspeed Ne, target fuel injection amount Qsol and real EGR rate Megrd.

In a step S112, the real EGR rate Megrd is compared with a predeterminedvalue MEGRLV#. The predetermined value MEGRLV# is a value fordetermining whether or not exhaust gas recirculation is actually beingperformed, and is set to, for example, 0.5%.

In the step S112, when Megrd>MEGRLV#, the routine proceeds to a stepS113. On the other hand, if Megrd≦MEGRLV#, the routine proceeds to astep S116. In order to treat the case of a very small exhaust gasrecirculation to be the same as the case where exhaust gas recirculationis not performed, the predetermined value MEGRLV# is not set to zero.

In the step S113, a target intake fresh air amount basic value tQacb iscalculated from the engine rotation speed Ne and real EGR rate Megrd bylooking up a map shown in FIG. 18. When the engine rotation speed Ne isconstant, this map gives a larger target intake fresh air amount basicvalue tQacb the larger the real EGR rate Megrd. This map is previouslystored in the memory of the control unit 41.

Next, in a step S114, a correction coefficient ktQac of the targetintake fresh air amount is calculated from the engine rotation speed Neand the target fuel injection amount Qsol by looking up a map shown inFIG. 19. The correction coefficient ktQac is a coefficient for settingthe target intake fresh air amount according to the running condition ofthe vehicle.

In a step S115, the target intake fresh air amount tQac is calculated bymultiplying the target intake fresh air amount basic value tQacb by thecorrection coefficient ktQac.

On the other hand, in the step S116, the target intake fresh air amounttQac when exhaust gas recirculation is not performed, is calculated fromthe engine rotation speed Ne and the target fuel injection amount Qsolby looking up a map shown in FIG. 20.

After calculating the target intake fresh air amount tQac in this way,the routine is terminated.

The control of the EGR amount of the EGR valve 6 as well as the controlof the supercharging pressure of the turbocharger 50 by the controller41 are performed based on these common parameters, the target fuelinjection amount Qsol, the time constant inverse value Kkin, the targetEGR rate Megr, the real EGR rate Megrd, the cylinder intake fresh airamount Qac, the real EGR amount Qec and the target intake fresh airamount tQac.

The control of the EGR amount is performed by controlling an openingarea of the EGR valve 6 to be equal to a target opening area Aev.

Next, the routine for calculating the target opening area Aev of the EGRvalve 6 for this control will be described referring to FIG. 37. Thisroutine is performed in synchronism with the REF signal.

First, the controller 41 reads a target EGR amount Tqec per cylinder inthe position of the EGR valve 6, an EGR amount feedback correctioncoefficient Kqac00 and the EGR valve flow velocity Cqe in a step S231.

These values are calculated by separate routines.

The target EGR amount Tqec per cylinder in the position of the EGR valve6 is calculated by the routine shown in FIG. 6. The EGR amount feedbackcorrection coefficient Kqac00 is calculated by a separate routine shownin FIG. 22, and a subroutine shown in FIG. 26. The EGR valve flowvelocity Cqe is calculated by the routine shown in FIG. 35.

These routines will first be described.

Referring to FIG. 6, firstly in a step S21, the controller 41 reads theintake fresh air amount Qacn at the inlet of a collector 3A. The intakefresh air amount Qacn per cylinder at the inlet of the collector 3A is avalue calculated by the step S33 of FIG. 7.

Next, in a step S22, the target EGR rate Megr is read. The target EGRrate Megr is a value calculated by the routine of FIG. 10.

Next, in a step S23, a required EGR amount Mqec is calculated byequation (9).

 Mqec=Qacn·Megr  (9)

In a next step S24, delay processing is performed on the required EGRamount Mqec by the following equation (10) using a time constant inversevalue Kkin calculated by the routine of FIG. 15, and this is convertedto an intermediate value corresponding to the required EGR amount percylinder in the intake valve position of the diesel engine 1.

Rqec=Mqec·Kkin+Rqec _(n−1)·(1−Kkin)  (10)

where,

Rqec_(n−1)=Rqec calculated on the immediately preceding occasion theroutine was performed.

In a next step S25, advance processing is performed by the followingequation (11) using the intermediate value Rqec and required EGR amountMqec, to calculate a target EGR amount Tqec per cylinder in the positionof the EGR valve 6.

Tqec=GKQEC·Mqec−(GKQEG−1)·Rqec _(n−1)  (11)

FIG. 22 shows the routine for calculating tile EGR amount feedbackcorrection coefficient Kqac00, an EGR flow velocity feedback correctioncoefficient Kqac0, and an EGR flow velocity learning correctioncoefficient Kqac.

This routine is performed in synchronism with the REF signal.

The EGR amount feedback correction coefficient Kqac00 read in a stepS231 of FIG. 37 is calculated by this routine.

First, in a step S131, the controller 41 first reads the target intakefresh air amount tQac, cylinder intake fresh air amount Qac, enginerotation speed Ne and target fuel injection amount Qsol.

In a step S132, a delay processing value tQacd of the target intakefresh air amount tQac is calculated using the following equation (12),from the target intake fresh air amount tQac and the time constantinverse value Kkin calculated by the routine of FIG. 15. The delayprocessing value tQacd corresponds to the target intake fresh air amountin the intake valve position of the diesel engine 1.

tQacd=tQac·Kkin·KQA#+tQacd _(n−1)·(1−Kkin·KQA#)  (12)

where,

KQA#=constant, and

tQacd_(n−1)=tQacd calculated on the immediately preceding occasion whenthe routine was executed.

In a following step S133, a feedback control permission flag fefb, alearning permission flag felrn and a learning value reflectionpermission flag felm2 which are related to the control of the EGR valveopening are read.

These flags are set by the independent routines shown in FIG. 23, FIG.24 and FIG. 25, respectively.

FIG. 23 shows the routine for setting the feedback control permissionflag fefb. This routine is performed at an interval of ten milliseconds.

Referring to FIG. 23, firstly in a step S271, the controller 41 readsthe engine rotation speed Ne, target fuel injection amount Qsol, realEGR rate Megrd and water temperature Tw.

In subsequent steps S152-S155, the EGR amount feedback controlconditions are determined.

In the step S152, it is determined whether or not the real EGR rateMegrd exceeds a predetermined value MEGRFB#. The predetermined valueMEGRFB# is a value for checking that exhaust gas recirculation isactually performed. In the step S153, it is determined whether or notthe cooling water temperature Tw exceeds a predetermined value TwFBL#.The predetermined value TwFBL# is set to 30° C. In a step S154, it isdetermined whether or not the target fuel injection amount Qsol exceedsa predetermined value QSOLFBL#.

The predetermined value QSOLFBL# is a value for checking that the dieselengine 1 is not in a fuel cut state. In a step S155, it is determinedwhether or not the engine rotation speed Ne exceeds a predeterminedvalue NeFBL#. The predetermined value NeFBL# is a value for checkingthat the vehicle is not in a low-speed region where the diesel engine 1stops rotation.

When all of the conditions of step S152-S155 are satisfied, the routineproceeds to a step S156 and increments a timer value Ctrfb.

In a following step S158, it is determined whether or not the timervalue Ctrfb is greater than a predetermined value TMRFB#. Thepredetermined value TMRFB# is set to, for example, a value less than onesecond. When the result of this determination is affirmative, theroutine sets the feedback control permission flag fefb to one in a stepS159, and the routine is terminated.

On the other hand, if any of the conditions of the steps S152-S155 isnot satisfied, in a step S157, the routine resets the timer value Ctrfbto zero, and proceeds to a following step S160.

When the determination of the step S158 is negative, the routine alsoproceeds to the step S160.

In the step S160, the feedback control permission flag fefb is reset tozero and the routine is terminated.

According to this routine, the feedback control permission flag fefb isset to one only when the state where all of the conditions of the stepsS152-S155 were satisfied, continues for a time exceeding thepredetermined value TMRFB#, and in other cases, the feedback controlpermission flag fefb is reset to zero.

FIG. 24 shows a routine for setting the learning value reflectionpermission flag felrn2. This routine is also performed at an interval often milliseconds.

Referring to FIG. 24, firstly in a step S161, the controller 41 readsthe engine rotation speed Ne, target fuel injection amount Qsol, realEGR rate Megrd and cooling water temperature Tw.

In subsequent steps S162-S165, EGR amount learning value reflectionconditions are determined.

In the step S162, it is determined whether or not the real EGR rateMegrd exceeds a predetermined value MEGRLN2#. The predetermined valueMEGRLN2# is a value for checking that exhaust gas recirculation isactually performed. In the step S163, it is determined whether or notthe cooling water temperature Tw exceeds a predetermined value TwLNL2#.The predetermined value TwLNL2#is set to 20° C. In the step S164, it isdetermined whether or not the target fuel injection amount Qsol exceedsa predetermined value QSOLLNL2#. The predetermined value QSOLLNL2# is avalue for checking that the diesel engine 1 is not in a fuel cut state.In the step S165, it is determined whether or not the engine rotationspeed Ne exceeds a predetermined value NeLNL2#. The predetermined valueNeLNL2# is a value for checking that the vehicle is not in a low-speedregion where the diesel engine 1 stops rotation.

Only when all of the conditions of step S162-S165 are satisfied, theroutine proceeds to a step S166 and increments a timer value Ctrln2.

In the following step S168 it is determined whether or not the timervalue Ctrln2 exceeds a predetermined value TMRLN2#. The predeterminedvalue TMRLN2# is set to 0.5 seconds. When the result of thisdetermination is affirmative, the routine sets the learning valuereflection permission flag felrn2 to one in a step S169, and the routineis terminated.

On the other hand, when any of the conditions of the steps S162-S165 isnot satisfied, in a step S167, the routine resets the timer value Ctrln2to zero, and proceeds to a following step S170. When the determinationof the step S168 is negative, the routine also proceeds to the stepS170.

In the step S170, the learning value reflection permission flag felrn2is reset to zero and the routine is terminated.

FIG. 25 shows the routine for setting the learning permission flagfelrn. This routine is also performed at an interval of tenmilliseconds.

Referring to FIG. 25, firstly in a step S171, the controller 41 readsthe engine rotation speed Ne, target fuel injection amount Qsol, realEGR rate Megrd, and water temperature Tw.

In subsequent steps S172-S177, the EGR amount learning permissionconditions are determined.

In the step S172, it is determined whether or not the real EGR rateMegrd exceeds a predetermined value MEGRLN#. The predetermined valueMEGRLN# is a value for checking that exhaust gas recirculation isactually performed. In the step S173, it is determined whether or notthe cooling water temperature Tw exceeds a predetermined value TwLNL#.The predetermined value TwLNL# is set to 70-80° C. In the step S174, itis determined whether or not the target fuel injection amount Qsolexceeds a predetermined value QSOLLNL#. The predetermined value QSOLLNL#is a value for checking that the diesel engine 1 is not in a fuel cutstate. In the step S175, it is determined whether or not the enginerotation speed Ne exceeds a predetermined value NeLNL#. Thepredetermined value NeLNL# is a value for checking that the vehicle isnot in a low-speed region where the diesel engine 1 stops rotation. Inthe step S176, it is determined whether or not the feedback controlpermission flag fefb is one. In the step S177, it is determined whetheror not the learning value reflection permission flag felrn2 is one.

Only when all of the conditions of the steps S172-S177 are satisfied,the routine proceeds to a step S178 and increments a timer value Ctrln.

In a following step S180, it is determined whether or not the timervalue Ctrln exceeds a predetermined value TMRLN#. The predeterminedvalue TMRLN# is set to four seconds. When the result of thisdetermination is affirmative, the routine sets the learning permissionflag felrn to one in a step S181, and the routine is terminated. On theother hand, if any of the conditions of the steps S172-S177 are notsatisfied, in a step S179, the routine resets the timer value Ctrln tozero, and proceeds to a following step S182. The routine also proceedsto the step S182 when the determination of the step S180 is negative. Inthe step S182, the learning permission flag felrn is reset to zero, andthe routine is terminated.

Referring again to FIG. 22, after reading this feedback controlpermission flag fefb, learning value reflection permission flag felrn2and learning permission flag felrn, in a step S134, the controller 41determines whether or not the feedback control permission flag fefb isone.

When the feedback control permission flag fefb is one, after calculatingthe feedback correction coefficient Kqac00 of the EGR amount in a stepS135, and the feedback correction coefficient Kqac0 of the EGR valveflow velocity Cqe in a step S136, the controller 41 proceeds to a stepS139.

On the other hand, when the feedback control permission flag fefb is notone in the step S134, the controller 41 sets the feedback correctioncoefficient Kqac00 of the EGR amount to one in a step S137, sets thefeedback correction coefficient Kqac0 to one in a following step S138,and then proceeds to the step S139.

Now, the calculation of the feedback correction coefficient Kqac00 ofthe EGR amount performed in the step S135 and the calculation of thefeedback correction coefficient Kqac0 of the EGR velocity performed inthe step S136, will be described.

The calculation of the feedback correction coefficient Kqac00 of the EGRamount is performed by a subroutine of FIG. 26.

Referring to FIG. 26, in a step S191, the controller 41 first reads thedelay processing value tQacd of the target intake fresh air amount,cylinder intake fresh air amount Qac, engine rotation speed Ne, targetfuel injection amount Qsol and the cooling water temperature Tw. Thedelay processing value tQacd is a value calculated in the step S132 ofFIG. 22.

In a step S192, a correction gain Gkfb of the EGR flowrate is calculatedby looking up a map shown in FIG. 27 previously stored in the memory ofthe controller 41, based on the engine rotation speed Ne and the targetfuel injection amount Qsol. In a following step S193, a watertemperature correction coefficient Kgfbtw of the correction gain iscalculated by looking up a map shown in FIG. 28 previously stored in thememory of the controller 41, based on the cooling water temperature Tw.

In a final step S194, the feedback correction coefficient Kqac00 of theEGR amount is calculated by the following equation (13), using thecorrection gain Gkfb and the water temperature correction coefficientKgfbtw.

Kqac 00=(tQacd/Qac−1)·Gkfb·Kgfbtw+1  (13)

(tQacd/Qac−1), the first term on the right hand side of equation (13),is an error ratio of the target intake fresh air amount delay processingvalue tQacd relative to the cylinder intake fresh air amount Qac.Therefore, the feedback correction coefficient Kqac00 of the EGR amountis a value centered on one.

The calculation of the feedback correction coefficient Kqac0 of the EGRvalve flow velocity is performed by a subroutine shown in FIG. 29.

Referring to FIG. 29, in a step S201, the controller 41 first reads thedelay processing value tQacd, cylinder intake fresh air amount Qac,engine rotation speed Ne, target fuel injection amount Qsol and thecooling water temperature Tw.

In a step S202, a correction gain Gkfbi of the EGR valve flow velocityis calculated by looking up a map shown in FIG. 30 previously stored inthe memory of the controller 41, based on the engine rotation speed Neand the fuel injection amount Qsol.

In a step S203, a water temperature correction coefficient Kgfbitw ofthe correction gain is calculated by looking up a map shown in FIG. 31previously stored in the memory of the controller 41, based on thecooling water temperature Tw. In a following step S204, an error ratioRqac0 is calculated by the following equation (14), using the correctiongain Gkfbi and the water temperature correction coefficient Kgfbitw.

Rqac 0=(tQacd/Qac−1)·Gkfbi·Kgfbitw+Rqac 0 _(n−1)  (14)

where,

Rqac0 _(n−1)=Rqac0 calculated on the immediately preceding occasion thesubroutine was executed.

In a following step S205, by adding one to the error ratio Rqac0, theEGR flow velocity feedback correction coefficient Kqac0 is calculated.Therefore, the feedback correction coefficient Kqac0 of the EGR valveflow velocity is a value proportional to the integral of the errorratio.

Now, referring again to FIG. 22, after setting the feedback correctioncoefficient Kqac00 of the EGR amount and the feedback correctioncoefficient Kqac0 of the EGR valve flow velocity, in the step S139, thecontroller 41 determines whether or not the learning value reflectionpermission flag felrn2 is one.

When the learning value reflection permission flag felrn2 is one, i.e.,when reflection in EGR amount control of the learning value ispermitted, in a step S140, the controller 41 reads the error ratiolearning value Rqac, by looking up a map shown in FIG. 32 previouslystored in the memory of the controller 41, based on the engine rotationspeed Ne and the target fuel injection amount Qsol. In a next step S141,the EGR flow velocity learning correction coefficient Kqac is calculatedby adding one to the error ratio learning value Rqac_(n).

When the learning value reflection permission flag felrn2 is not one inthe step S139, the controller 41 sets the EGR flow velocity learningcorrection coefficient Kqac to one in a step S142.

After the processing of the step S141 or step S142, in a step S143, thecontroller 41 determines whether or not the learning permission flagfelrn is one.

When the learning permission flag felrn is one, in a step S144, thecontroller 41 subtracts one from the EGR flow velocity feedbackcorrection coefficient Kqac0 to calculate the current value Rqacp of theerror ratio. In a following step S146, the learning value is updatedusing the subroutine of FIG. 33, and the routine is terminated.

When the learning permission flag felrn is not one, in a step S145, thecontroller 41 resets the current value Rqacp of the error ratio to zero,and terminates the routine of FIG. 22.

Next, the updating of the learning value performed in the step S146 willbe described.

Referring to FIG. 33, in a step S211, the controller 41 first reads theengine rotation speed Ne, target fuel injection amount Qsol and errorratio Rqacp calculated in the step S144 of FIG. 22.

In a step S212, a learning rate Tclrn is calculated by looking up a mapshown in FIG. 34 previously stored in the memory of the controller 41,based on the engine rotation speed Ne and target fuel injection amountQsol.

In a step S213, the error ratio learning value Rqac_(n) is calculated bylooking up the aforesaid map of FIG. 32, based on the engine rotationspeed Ne and target fuel injection amount Qsol.

In a following step S214, weighted average processing by the followingformula (15) is added to the error ratio Rqacp read in the step S211,and updating of the error ratio learning value is performed.

Rqac _(n)(new=Rqacp·Tclrn+Rqac _(n)(old)·(1−Tclrn)  (15)

where,

Rqac_(n)(new)=error ratio learning value Rqac_(n) to be written on themap,

Rqacp=error ratio read in the step S211, and

Rqac_(n)(old)=error ratio learning value Rqac_(n) read from the map inthe step S213.

In a next step S215, the stored value of the map of FIG. 32 isoverwritten using the error ratio learning value Rqac_(n)(new)calculated in this way.

By terminating the subroutine of FIG. 33, the controller 41 terminatesthe processing of the routine of FIG. 22.

Next, referring to FIG. 35, a routine for calculating the EGR valve flowvelocity Cqe will be described.

First, in a step S221, the controller 41 reads the real EGR amount Qec,real EGR rate Megrd and cylinder intake fresh air amount Qac.

In a next step S222, the controller 41 reads the feedback correctioncoefficient Kqac0 of the EGR valve flow velocity and EGR flow velocitylearning correction coefficient Kqac.

In a next step S223, a corrected real EGR amount Qec_h is calculated bythe following equation (16)

Qec _(—) h=Qec·Kqac·Kqac 0  (16)

In steps S224-S227, an initial value of the corrected real EGR amountQec_h when EGR operation begins, is set. In the step S224, it isdetermined whether or not the corrected real EGR amount Qec_h is zero.When Qec_h is zero, i.e. when EGR is not operating, the corrected realEGR amount Qec_h is set by the following equation (17) in a step S225,and the routine proceeds to a step S226. When the corrected real EGRamount is not zero in the step S224, the routine bypasses the step S225and proceeds to the step S226.

Qec _(—) h=Qac·MEGRL#  (17)

where,

MEGRL#=constant.

In the step S226, it is determined whether or not the real EGR rateMegrd is zero. When the real EGR rate Megrd is zero, the real EGR rateMegrd is set equal to the constant MEGRL# in the step S227, and theroutine proceeds to a step S228. When the real EGR rate Megrd is notzero, the routine bypasses the step S227 and proceeds to the step S228.

When the EGR valve 6 is fully closed, the EGR valve flow velocity of theEGR valve 6 is zero, and equations (16) and (17) are equations forsetting the initial value of parameters used for flow velocitycalculations when EGR operation starts, i.e., when the EGR valve 6begins to open. The constant MEGRL# may be set to, for example, 0.5.

The differential pressure upstream and downstream of the EGR valve 6when EGR operation starts is different according to the runningconditions of the diesel engine 1, and as a result, the EGR valve flowvelocity when EGR operation starts also differs. The differentialpressure upstream and downstream of the EGR valve 6 when the EGR valve 6begins to open, depends on the cylinder intake fresh air amount Qac.Thus, the calculation precision of the EGR valve flow velocity when EGRoperation starts, can be improved by making the initial value of Qec_hdirectly proportional to the cylinder intake fresh air amount Qac byequation (17).

Now, in the step S228, the controller 41 calculates the EGR valve flowvelocity Cqe by looking up a map shown in FIG. 36 which is previouslystored in the memory of the controller 41, based on the corrected realEGR amount Qec_h and real EGR rate Megrd, and the routine is terminated.

In the step S231 of FIG. 37, the target EGR amount Tqec per cylinder inthe position of the EGR valve 6, the EGR amount feedback correctioncoefficient Kqac00 and the EGR valve flow velocity Cqe which werecalculated by the above separate routines, are read.

In a next step S232, the target EGR amount Tqec per cylinder in theposition of the EGR valve 6 is converted into a target EGR amount Tqekper unit time by the following equation (18). $\begin{matrix}{{Tqek} = {{Tqec} \cdot \frac{\left( \frac{Ne}{{KCON}\quad \#} \right)}{Kqac00}}} & (18)\end{matrix}$

where,

Kqac00=EGR amount feedback correction coefficient.

In a step S233, the target opening area Aev of the EGR valve 6 iscalculated by the following equation (19), and the routine isterminated. $\begin{matrix}{{Aev} = \frac{Tqek}{Cqe}} & (19)\end{matrix}$

The target opening area Aev of the EGR valve 6 thus obtained is changedinto a lift amount of the EGR valve 6 by searching a map having thecontents shown in FIG. 5 which is prestored in the controller 41.

The controller 41 outputs a duty control signal to the pressure controlvalve 56 so that the lift amount of the EGR valve 6 coincides with thisvalue.

On the other hand, control of the supercharging pressure of theturbocharger 50 is performed by varying the opening rate of the variablenozzle 53 by outputting a signal representing a duty value Dtyvnt to thepressure control valve 56.

The routine for calculating the duty value Dtyvnt used for his controlwill now be described referring to FIG. 38. This routine is performedevery ten milliseconds. This routine comprises various subroutines.

First, in a step S241, the controller 41 performs an overboostdetermining flag setting subroutine shown in FIG. 39.

Referring to FIG. 39, in a step S251, the controller 41 first reads anengine rotation speed Ne, target fuel injection amount Qsol, cylinderintake fresh air amount Qac, these values Ne_(n−k), Qsol_(n−k) andQac_(n−k) when the subroutine was performed on k preceding occasions,and the real EGR rate Megrd.

In a step S252, a cylinder intake gas amount Qcyl (mg) per one strokecycle of the diesel engine 1 is calculated by the following equation(20) using the cylinder intake fresh air amount Qac and real EGR rateMegrd. $\begin{matrix}{{Qcyl} = {{Qac} \cdot \left( {1 + \frac{Megrd}{100}} \right)}} & (20)\end{matrix}$

The second term ${Qac} \cdot \frac{Megrd}{100}$

on the right-hand side of equation (20) is the real EGR amount, and thevalue obtained by adding this real EGR amount to the cylinder intakefresh air amount Qac is the gas amount aspirated per stroke cycle by onecylinder of the diesel engine.

The real EGR amount Qec calculated by the routine of FIG. 21 may be usedas the real EGR amount. In this case, Qcyl=Qac+Qec.

In a step S253, the real exhaust gas amount Qexh per stroke cycle (mg)is calculated by the following equation (21). $\begin{matrix}{{Qexh} = {\left( {{Qac} + {{{Qsol} \cdot {GKQFVNT}}\quad \#}} \right) \cdot \frac{Ne}{{KCON}\quad \#}}} & (21)\end{matrix}$

where,

GKQFVNT#=scale factor (mg/mm³), and

KCON#=constant.

Here, the difference in the temperature of intake air and exhaust gas isdisregarded, and the sum total of the exhaust gas due to combustion ofthe fuel of the target fuel injection amount Qsol and the cylinderintake fresh air amount Qac is considered to be the exhaust gas amount.

The unit of the target fuel injection amount Qsol is (mm³), and this isconverted into mass by multiplying by the conversion factor GKQFVNT#.Further, the mass per stroke cycle (mg) is converted into a mass persecond (g) by multiplying by $\frac{Ne}{{KCON}\quad \#}.$

In a step S254, the difference of engine rotation speed Ne, target fuelinjection amount Qsol, cylinder intake fresh air amount Qac and thevalues Ne_(n−k), Qsol_(n−k) and Qac_(n−k) when the subroutine wasperformed k occasions ago, is calculated as an engine rotation speedvariation DNE, fuel injection amount variation amount DQSOL and cylinderintake fresh air amount variation DQAC, respectively.

In steps 255-S257, based on these values, it is determined whether ornot overboost will occur.

In the step S255, it is determined whether or not the engine rotationspeed Ne is larger than a predetermined value KNEOB#, and the enginerotation speed variation DNE is larger than a predetermined valueKDNEOB#.

In the step S256, it is determined whether or not the target fuelinjection amount Qsol is larger than a predetermined value KQFOB#, andwhether a fuel injection variation amount DQSOL is larger than apredetermined value KDQFOB#.

In the step S257, it is determined whether the cylinder intake fresh airamount DQAC is larger than a predetermined value KDQACOB#.

If any of the conditions of the steps 255-S257 are satisfied, it isconsidered that overboost occurs. In this case, the subroutine proceedsto a step S261.

On the other hand, when all the determination results of the stepsS255-S257 are negative, the subroutine proceeds to a step S258.

Here, the controller 41 calculates a corresponding overboost determiningintake gas amount TQcyl referring to a map having the contents shown inFIG. 41 which is prestored in the controller 41, based on a real exhaustgas amount Qexh calculated in the step S253.

In FIG. 41, the overboost determining intake gas amount TQcyl has asubstantially convex-shaped pattern relative to the real exhaust gasamount Qexh.

This characteristic will be described referring to FIG. 42.

This diagram shows the relation of the real exhaust gas amount Qexh,pressure ratio Pm/Pa and effectiveness η of the turbocharger taking thepressure of the intake manifold 3B as Pm, and atmospheric pressure asPa.

The effectiveness η is equivalent to a fresh air amount, and the higherthe effectiveness η, the more the fresh air amount aspirated by thediesel engine 1 from the intake passage 3 increases.

When the real exhaust gas amount Qexh increases as shown in this figure,the effectiveness increases up to a certain region under the samepressure ratio Pm/Pa, but if the real exhaust gas amount Qexh increasesbeyond this region, the effectiveness η will fall.

In FIG. 41, the overboost determining intake gas amount TQcyl changes toa convex type for reflecting the above-mentioned characteristics of theeffectiveness η. Also, in the map of FIG. 41, for the same real exhaustgas amount Qexh, the overboost determining intake gas amount TQcyl takesa smaller value the lower the atmospheric pressure.

Now, In the step S259, it is determined whether or not the cylinderintake gas amount Qcyl (mg) per stroke cycle of the diesel engine 1calculated in the step S252 is higher than the overboost determiningintake gas amount TQcyl. When this condition is satisfied, thesubroutine proceeds to a step S261.

In the step S261, the overboost determining flag FOVBT is set to one, anoverboost timer TMROB is reset to zero in the following step S262, andthe subroutine is terminated.

On the other hand, in the step S259, when the cylinder intake gas amountQcyl (mg) per stroke cycle of the diesel engine 1 is less than theoverboost determining intake gas amount Tqcyl, the subroutine resets theoverboost determining flag FOVBT to zero in a step S260, and the routineis terminated. Here, FOVBT=1 shows that control of overboost isrequired, and FOVBT=0 shows that there is no possibility of overboost.

The overboost determining flag FOVBT is used for suppression in asubroutine for setting the target opening rate Rvnt of the variablenozzle 53 of the turbocharger 50 described later.

The overboost timer TMROB shows the elapsed time after the overboostdetermining flag FOVBT changes to one from zero.

The change of the accelerator opening Cl and the overboost determiningflag FOVBT will now be described, referring to FIGS. 40A-40E.

When the accelerator pedal is sharply depressed as shown in FIG. 40A,firstly, the target fuel injection amount Qsol changes as shown in FIG.40B, the engine rotation speed Ne changes as shown in FIG. 40C, and thecylinder intake fresh air amount Qac changes as shown in FIG. 40D.

According to the subroutine of FIG. 39, whenever the target fuelinjection amount Qsol, engine rotation speed Ne or cylinder intake freshair amount Qac vary largely, the overboost determining flag FOVBT is setto one.

If determination of overboost is performed depending only on thecylinder intake fresh air amount Qac, the suppression operation may betoo late for generation of the overboost, hence according to thisinvention, the delay in the determination is prevented by adding thetarget fuel injection amount Qsol and engine rotation speed Ne, whichhave an earlier reaction, to the basis for determination of overboost.

In FIGS. 40A-40E, a smoke limit is introduced in the target fuelinjection amount Qsol.

That is, as the change in the cylinder intake fresh air amount Qac islate for the change of accelerator opening, if the target fuel injectionamount Qsol is made to increase rapidly according to the change ofaccelerator opening, smoke will be produced.

Hence, a restriction is applied to the amount of increase of the targetfuel injection amount Qsol. This restriction is the smoke limit, and theincrease in the target fuel injection amount Qsol is separated into twophases in FIG. 40B due to the smoke limit.

Now, referring again to FIG. 38, the controller 41 sets a suppressionrelease flag FCLROB by a subroutine shown in FIG. 43 in a step S242.

The suppression release flag FCLROB is introduced due to the followingreasons.

Overboost suppression is performed over a predetermined time.

After the predetermined time passes, when the variable nozzle 53 isimmediately driven in the closing direction and the superchargingpressure is increased, it may give rise to overboost.

Hence, the suppression release flag FCLROB is introduced, and as shownin FIGS. 44A and 44B, when the overboost determining flag FOVBST changesfrom one through zero, the suppression release flag FCLROB is changedover from zero to one.

The opening of the variable nozzle 53 is slowly returned to the openingbefore the suppression of overboost took place in the period when thesuppression release flag FCLROB is one.

The above control will be described referring to FIG. 43.

In a step S271, the controller 41 determines whether or not theoverboost timer TMROB is below a predetermined suppression periodTTMROB, or whether or not the overboost determining flag FOVBST is one

When either of the above conditions is satisfied, it is considered thatoverboost suppression control is underway.

In this case, in a step S274, the subroutine continues the state whereinthe overboost determining flag FOVBST=1, and the subroutine isterminated.

When neither of the conditions of step S271 is satisfied, it isconsidered that overboost suppression control is not being performed. Inthis case, the subroutine proceeds to a step S272.

In the step S272, the overboost determining flag FOVBST is reset tozero, and an overboost clear timer TMRCLROB is reset to zero in afollowing step S273.

The overboost clear timer TMRCLROB shows the elapsed time after theoverboost determining flag FOVBST changes to zero from one.

In a following step S275, it is determined whether or not the overboostclear timer TMRCLROB is less than a predetermined suppression releaseperiod TTMRCLROB.

When the determination result of the step S275 is affirmative, thesubroutine proceeds to a step S277, and when it is negative, thesubroutine proceeds to a step S276.

In the step S277, the suppression release flag FCLROB is set to one, andthe subroutine is terminated.

In the step S276, the suppression release flag FCLROB is reset to zero,and the subroutine is terminated.

When the suppression release flag FCLROB is reset to zero, overboostsuppression control is terminated and normal operation of the dieselengine 1 is performed thereafter.

On the other hand, immediately after resetting the overboost determiningflag FOVBST to zero in the step S272, the determination result of thestep S275 must be affirmative, and the suppression release flag FCLROBchanges from zero to one due to operation in the step S277 at this time.

The suppression period TTMROB used in the step S271 is calculated by theseparate routine shown in FIG. 45. Also, the suppression release periodTTMRCLROB used in step S275 is calculated by the separate routine shownin FIG. 48. Each of these separate routines is performed every tenmilliseconds.

First, referring to FIG. 45, the controller 41 calculates a suppressionperiod basic value TTMROB0 by looking up a map shown in FIG. 46 from theengine rotation speed variation DNE and fuel injection variation amountDQSOL in a step S281.

In a following step S282, a correction coefficient KTMROB of thesuppression period is calculated referring to a prestored map in thecontroller 41 whereof the contents are shown in FIG. 47.

The correction coefficient KTMROB of suppression period is set based onthe difference of the cylinder intake fresh air amount variation DQAC,cylinder intake gas amount Qcyl, and overboost determining intake gasamount TQcyl.

In a step S283, the suppression period TTMROB is calculated bymultiplying the suppression period basic value TTMROB0 by the correctioncoefficient KTMROB.

The engine rotation speed variation DNE, the fuel injection variationamount DQSOL and the cylinder intake fresh air amount variation DQA arecalculated by the same method as that of the step S254 of FIG. 39.

The cylinder intake gas amount Qcyl is calculated by the same method asthat of the step S252 of FIG. 39.

The overboost determining intake gas amount TQcyl is calculated by thesame method as that of the step S258 of FIG. 39.

In FIG. 46, the reason why the suppression period basic value TTMROB0 isincreased the larger the engine rotation speed variation DNE or thecylinder intake fresh air amount variation DQAC, is because overboostoccurs more easily the larger the variation of the engine rotation speedNe or the target fuel injection amount Qsol which represent the engineload.

In FIG. 47, the reason why the correction coefficient KTMROB isincreased the larger the cylinder intake fresh air amount variation DQACor the difference between the cylinder intake gas amount Qcyl and theoverboost determining intake gas amount Tqcyl, is because overboostoccurs more easily the larger the cylinder intake fresh air amountvariation DQAC or the difference between the cylinder intake gas amountQcyl and the overboost determining intake gas amount TQcyl.

Next, referring to FIG. 48, the suppression release period basic valueTTMRCLR is calculated in a step S291 from the atmospheric pressure Padetected by the atmospheric pressure sensor 38 and a prestored map inthe controller 41 whereof the contents are shown in FIG. 49.

In FIG. 49, the reason why the suppression release period basic valueTTMRCLROB0 is increased the lower the atmospheric pressure Pa, is asfollows.

The exhaust gas amount of the diesel engine 1 is larger, the larger thedifference of the exhaust pressure and atmospheric pressure.

If the exhaust pressure is fixed, the exhaust gas amount is larger thelower the atmospheric pressure Pa. The work which the turbocharger 50performs also becomes large, and it becomes easy to produce anoverboost.

Hence, the suppression release period basic value TTMRCLROB0 isincreased the lower the atmospheric pressure Pa. A typical conditionunder which the atmospheric pressure Pa is low, is running on highground.

In a following step S292, the suppression release period correctioncoefficient KTMRCLROB is calculated from the real exhaust gas amountQexh, referring to a prestored map in the controller 41 whereof thecontents are shown in FIG. 50.

In FIG. 50, when the real exhaust gas amount Qexh increases beyond acertain level, the correction coefficient KTMRCLROB increases because itbecomes easy to generate an overboost from this level.

In a following step S293, the suppression release period TTMRCLROB iscalculated by multiplying the suppression release period basic valueTTMRCLROB0 by the suppression release period correction coefficientKTMRCLROB.

Referring again to FIG. 38, after setting the suppression release flagFCLROB in the step S242, the controller 41 determines the target openingrate Rvnt of the variable nozzle 53 using a subroutine shown in FIG. 51in the step S243.

The opening rate of the variable nozzle 53 is a numerical value whichexpresses, as a percentage, the ratio of the opening cross-sectionalarea to the opening cross-sectional area when the variable nozzle 53 isfully open.

In the fully open state, the opening rate is 100%, and in the closedstate, the proportion is 0%. Although the opening rate is used as ageneral value to represent the opening of the variable nozzle 53regardless of the relation with the capacity of the turbocharger 50, itis of course also possible to replace the opening rate by the openingarea.

The turbocharger 50 used with this device is so constructed that thesupercharging pressure is higher the smaller the opening rate of thevariable nozzle 53. When the variable nozzle 53 is fully open, thesupercharging pressure is a minimum, and when the variable nozzle 53 isfully closed, the supercharging pressure is a maximum, for a givenexhaust gas amount.

Now, referring to FIG. 51, firstly in a step S301, the controller readsthe target intake fresh air amount tQac, real EGR amount Qec, enginerotation speed Ne, target fuel injection amount Qsol and target EGR rateMegr.

In a following step S302, an intake fresh air amount equivalent valuetQas0 for calculating the target opening rate Rvnt of the variablenozzle 53 is calculated by the following equation (22). $\begin{matrix}{{tQas0} = {\left( {{tQac} + {{{Qsol} \cdot {QFGAN}}\quad \#}} \right) \cdot \frac{Ne}{{KCON}\quad \#}}} & (22)\end{matrix}$

where,

QFGAN#=gain, and

KCON#=constant.

In a following step S303, an EGR amount equivalent value Qes0 forcalculating the target opening rate Rvnt of the variable nozzle 53 iscalculated by the following equation (23). $\begin{matrix}{{Qes0} = {\left( {{Qec} + {{{Qsol} \cdot {QFGAN}}\quad \#}} \right) \cdot \frac{Ne}{{KCON}\quad \#}}} & (23)\end{matrix}$

In equations (22) and (23), Ne/KCON# is a multiplier for changing thefresh air amount or the EGR amount per cylinder into a value per unittime.

Also, in equations (22) and (23), Qsol×QFGAN# is added to the targetintake fresh air amount tQac or the real EGR amount Qec for changing thetarget opening rate Rvnt according to the load of the diesel engine 1.

Herein, the target fuel injection amount Qsol is considered to representthe engine load, and the effect of the engine load is adjusted by thegain QFGAN#.

In the following description, tQas0 calculated in this way is referredto as a set intake fresh air amount equivalent value, and Qes0 isreferred to as a set EGR amount equivalent value.

In a following step S304, it is determined whether or not the target EGRrate Megr is greater than a predetermined value KEMRAV#.

The predetermined value KEMRAV# is a value for determining from thetarget EGR rate Megr whether or not exhaust gas recirculation isactually performed.

When the target EGR rate Megr is larger than the predetermined valueKEMRAV#, it is determined whether or not the overboost determining flagFOVBST is one in a step S305.

When the target EGR rate Megr is less than the predetermined valueKEMRAV#, it is determined whether or not the overboost determining flagFOVBST is one in a step S306.

When the target EGR rate Megr is larger than the predetermined valueKEMRAV# and the overboost determining flag FOVBST is one, it indicatesthat exhaust gas recirculation is performed and overboost suppression isrequired.

In this case, the subroutine proceeds to a step S307.

In the step S307, based on the set intake fresh air amount equivalentvalue tQas0 and the set EGR amount equivalent value Qes0, the targetopening rate basic value Rvnt0 of the variable nozzle 53 is calculatedby looking up a map prestored in the controller 41 whereof the contentsare shown in FIG. 52.

When the target EGR rate Megr is larger than the predetermined valueKEMRAV# and the overboost determining flag FOVBST is not one, itindicates that exhaust gas recirculation is performed but overboostsuppression is not required. In this case, the subroutine proceeds to astep S308.

In the step S308, based on the set intake fresh air amount equivalentvalue tQas0 and the set EGR amount equivalent value Qes0, the targetopening rate basic value Rvnt0 of the variable nozzle 53 is calculatedby looking up a map prestored in the controller 41 whereof the contentsare shown in FIG. 53.

In the maps of FIGS. 52 and 53, the target opening rate basic valueRvnt0 is set to decrease as the set EGR amount equivalent value Qes0increases, due to the following reason.

If the EGR amount increases, the fresh air amount will become lessrelatively. The air-fuel ratio inclines to the rich side due toreduction in the fresh air amount, and the diesel engine 1 easilygenerates smoke. To prevent smoke, it is necessary to increase thesupercharging pressure of the turbocharger 50 and to ensure the freshair amount. Thus, the target opening rate basic value Rvnt0 is decreasedas the EGR amount increases.

The characteristics of the maps of FIGS. 52 and 53 differ depending onwhether fuel cost-performance, exhaust composition or accelerationperformance is stressed. These characteristics will be describedreferring to FIGS. 59A-59C.

The diagrams of FIGS. 59A-59C, show how fuel consumption, nitrogenoxides (NOx), particulates (PM) and intake fresh air amount varyrelative to the opening area of the variable nozzle 53 in the case wherethe EGR rate is large and the case where it is small, when the enginerotation speed and engine torque are kept constant. The intake fresh airamount corresponds to the fuel injection amount, and the fuel injectionamount represents the acceleration performance of the vehicle.

From these diagrams, it is seen that the opening area for minimizingfuel consumption, the opening area for optimizing exhaust compositionand the opening area for maximizing acceleration performance, aredifferent.

If fuel consumption is stressed, for example, the opening area of thevariable nozzle 53 which minimizes fuel consumption is calculated forvarious engine speeds and engine torques, and the maps of FIGS. 52, 53are generated based on this data.

When the target EGR rate Megr is smaller than the determined valueKEMRAV# in the step S304 and the overboost determining flag FOVBST isone in the step S306, it indicates that exhaust gas recirculation iseffectively not performed but overboost suppression is required. In thiscase, the subroutine proceeds to a step S310. In the step S310, based onthe set intake fresh air amount equivalent value tQas0 and the targetfuel injection amount Qsol, the target opening rate basic value Rvnt0 ofthe variable nozzle 53 is calculated referring to a map prestored in thecontroller 41 whereof the contents are shown in FIG. 54.

When the target EGR rate Megr is smaller than the predetermined valueKEMRAV# in the step S304 and the overboost determining flag FOVBST isnot one in the step S306, it indicates that exhaust gas recirculation iseffectively not performed and overboost suppression is unnecessary. Inthis case, the subroutine proceeds to a step S309.

In the step S309, based on the set intake fresh air amount equivalentvalue tQas0 and the target fuel injection amount Qsol, the targetopening rate basic value Rvnt0 of the variable nozzle 53 is calculatedreferring to a map prestored in the controller 41 whereof the contentsare shown in FIG. 55.

The maps of FIG. 52 and FIG. 54 applied during overboost suppressiongive a larger target opening rate basic value Rvnt0 than the maps ofFIG. 53 and FIG. 55 applied during normal running.

In order to suppress the overboost, the supercharging pressure has to beweakened, so Rvnt0 is increased to increase the opening of the variablenozzle 53.

In the maps of FIGS. 52, 53, the target opening rate basic value Rvnt0is set based on the intake fresh air amount equivalent value tQas0 andthe set EGR amount equivalent value Qes0, but it is also possible to setthe target opening rate basic value Rvnt0 based on the target intakefresh air amount tQac and the real EGR amount Qec.

Further, it is also possible to set the target opening rate basic valueRvnt0 based on the target intake fresh air amount tQac and the EGRamount Qec0 per cylinder at the inlet of the collector 3A.

In the transient running state of the diesel engine 1, the EGR amountQec0 per cylinder at the inlet of the collector 3A varies in a stepwisemanner, and there is a delay until the real EGR amount Qec catches upwith the target value. Due to a deviation in the EGR amount equivalentto this delay, an error arises in the target opening rate basic valueRvnt0.

When the target opening rate basic value Rvnt0 is set, by using the realEGR amount Qec that was obtained by performing delay processing on theEGR amount Qec0 per cylinder at the inlet of the collector 3A, a targetintake fresh air amount optimized for one of the preselected fuelconsumption, discharge composition and acceleration characteristics isobtained, even when the diesel engine 1 is in a transient running state.

Thus, after calculating the target opening rate basic value Rvnt0, in astep S311, it is determined whether or not the suppression release flagFCLROB is one.

When the suppression release flag FCLROB is not one (i.e., when the flagFCLROB is zero), it shows that the current running state is not in theoverboost suppression release period.

In this case, the target opening rate Rvnt is set equal to the targetopening rate basic value Rvnt0, and the subroutine is terminated.

When the suppression release flag FCLROB is one, it shows that thecurrent running state is in the suppression release period.

In this case, the target opening rate Rvnt is set by equation (24), andthe subroutine is terminated. $\begin{matrix}{{Rvnt} = {{\frac{1}{{TMRCLROB}\quad \#} \cdot {Rvnt0}} + {\left( {1 - \frac{1}{{TMRCLROB}\quad \#}} \right) \cdot {Rvnt}_{n - 1}}}} & (24)\end{matrix}$

where,

TMRCLROB#=time constant, and

Rvnt_(n−1)=Rvnt calculated on immediately preceding occasion when thesubroutine was executed.

Thus, generation of overboost is prevented by restricting the closingrate of the variable nozzle 53 by equation (24) during the suppressionrelease period.

Referring again to FIG. 38, after determining the target opening rateRvnt of the variable nozzle 53 in the step S243, in a following step8244, the controller 41 performs advance processing on the targetopening rate Rvnt taking account of the dynamics of the intake airsystem using a routine shown in FIG. 60. This routine is performed at aninterval of ten milliseconds.

The response delay after outputting a duty signal to the pressurecontrol valve 56 until the intake fresh air amount changes, includes agas flow lag depending on the turbo lag and the flowrate of intake airand exhaust gas, and the response delay of the pressure actuator 54. Thetime constant of the gas flow lag varies depending on the exhaust gasamount of the diesel engine 1, but the time constant of the responsedelay of the pressure actuator 54 is fixed.

In this control device, high control precision is obtained bycalculating these delays individually and compensating each responsedelay individually in the control of the opening rate of the variablenozzle 53. Advance processing of the target opening rate Rvnt of stepS244 is performed in order to compensate the gas flow lag.

The correction of the response delay of the actuator 54 is performedseparately and is described later.

Referring to FIG. 60, the controller 41, in a step S321, first reads thetarget opening rate Rvnt, the delay processing value tQacd of the targetintake fresh air amount which was calculated by the routine of FIG. 22,the target fuel injection amount Qsol and the engine rotation speed Ne.In a following step S322, the cylinder exhaust gas amount Tqexhd (mg)per stroke cycle of the diesel engine 1is calculated by the followingequation (25). $\begin{matrix}{{Tqexh} = {\left( {{tQacd} + {{{Qsol} \cdot {QFGAN}}\quad \#}} \right) \cdot \frac{Ne}{{KCON}\quad \#}}} & (25)\end{matrix}$

where,

QFGAN#=gain, and

KCON#=constant.

Equation (25) is equivalent to an equation wherein the target intakefresh air amount tQac on the right-hand side of equation (22) isreplaced by the delay processing value tQacd of the target intake freshair amount. Consequently, the cylinder exhaust gas amount Tqexhd perstroke cycle of the diesel engine 1 obtained instead of the set intakefresh air amount equivalent value tQas0, varies under a time constantset assuming variation of the actual exhaust gas amount. Hence, thecylinder exhaust gas amount Tqexhd per stroke cycle of the diesel engine1 is referred to as a real exhaust gas amount equivalent value.

FIGS. 61A-61D show the variation of the set intake fresh air amountequivalent value tQas0 and the real exhaust gas amount equivalent valueTqexhd when the target fuel injection amount Qsol is increased in steps.It was confirmed by experiments performed by the Inventors that thevariation of the real exhaust gas amount equivalent value Tqexhd of FIG.61D relative to the target fuel injection amount Qsol of FIG. 61Bclosely follows the variation of the actual exhaust gas amount shown bythe broken line in this figure.

In a following step S323, the target opening rate Rvnt is compared withan opening prediction value Cavnt_(n−1) calculated on the immediatelypreceding occasion the routine was performed. An opening predictionvalue Cavnt is a weighted average value of the target opening rate Rvnt.

Here, the target opening rate Rvnt is a value which varies in stepwisefashion, and the opening prediction value Cavnt is a value which variessmoothly.

Therefore, when the target opening rate Rvnt is larger than Cavnt_(n−1),it shows that the variable nozzle 53 is operating in the openingdirection. When the target opening rate Rvnt is smaller thanCavnt_(n−1), it shows that the variable nozzle 53 is operating in theclosing direction.

Hence, when the target opening rate Rvnt is larger than Cavnt_(n−1), ina step S324, the routine calculates an advance correction gain TGKVNTOwhen the variable nozzle 53 operates in the opening direction from thereal exhaust gas amount equivalent value Tqexhd referring to a maphaving the contents shown in FIG. 62 which is prestored in thecontroller 41, and sets TGKVNTO to an advance correction gain Gkvnt.

In the following step S325, the time constant equivalent value TTCVNTOof the advance correction when the variable nozzle 53 operates in theopening direction is calculated from the real exhaust gas amountequivalent value Tqexhd referring to a map having the contents shown inFIG. 64 which is prestored in the controller 41, and TTCVNTO is set asan advance correction constant equivalent value Tcvnt. After thisprocessing, the routine proceeds to a step S331.

On the other hand, in the step S323, when the target opening rate Rvntis not larger than Cavnt_(n−1) on the immediately preceding occasionwhen the routine was performed, it is determined whether or not thetarget opening rate Rvnt is smaller than the opening prediction valueCavnt_(n−1) in the step S326.

When the target opening rate Rvnt is smaller than Cavnt_(n−1), in a stepS327, the advance correction gain TGKVNTC when the variable nozzle 53operates in the closing direction, is calculated from the real exhaustgas amount equivalent value Tqexhd, referring to a map having thecontents shown in FIG. 63 which is prestored in the controller 41, andTGKVNTC is set as the advance correction gain Gkvnt.

In a next step S328, the advance correction time constant equivalentvalue TTCVNTC when the variable nozzle 53 operates in the closingdirection is calculated from the real exhaust gas amount equivalentvalue Tqexhd referring to a map whereof the contents are shown in FIG.65 which is prestored in the controller 41, and TTCVNTC is set to theadvance correction constant equivalent value Tcvnt. After thisprocessing, the routine proceeds to the step S331.

In the step S326, the case when the target opening rate Rvnt is not lessthan the estimated opening rate Cavnt_(n−1), is the case when the targetopening proportion Rvnt is equal to the estimated opening rateCavnt_(n−1). In this case, the advance correction gain Gkvnt is setequal to the value Gkvnt_(n−1) on the immediately preceding occasion theroutine was executed, in a step S329. Likewise, the advance correctiontime constant equivalent value Tcvnt is set equal to the valueTcvnt_(n−1) on the immediately preceding occasion the routine wasexecuted, in a step S330. After this processing, the routine proceeds tothe step S331.

The advance correction gains TGKVNTO, TGKVNTC shown in the maps of FIG.62 and FIG. 63 may be divided into a region near 1.0, a region clearlylarger than 1.0, and a region clearly smaller than 1.0 according to areal exhaust gas amount equivalent value Tqexh.

The region where TGKVNTO, TGKVNTC are clearly larger than 1.0 isreferred to as a small exhaust gas amount region. The region whereTGKVNTO, TGKVNTC are clearly smaller than 1.0 is referred to as a largeexhaust gas amount region. The region where TGKVNTO, TGKVNTC are near1.0 is referred to as an intermediate region. The intermediate region isset in order to prevent the correction gain from abruptly varying at1.0, and to vary it gradually. In this embodiment, an exhaust gas amountregion where the ratio of the exhaust gas amount with respect to themaximum exhaust gas amount is less than 30% is set to the small exhaustgas amount region, while an exhaust gas amount region where the ratio ofthe exhaust gas amount with respect to the maximum exhaust gas amount islarger than 60% is set to the large exhaust gas amount region.

A small exhaust gas amount region is a region where the chargingefficiency increases together with the increase in the exhaust gasamount of the diesel engine 1, and a large exhaust gas amount region isa region wherein the charging efficiency decreases together with theincrease in the exhaust gas amount of the diesel engine 1.

These regions are determined as follows.

Referring to FIG. 100, it is known that the charging efficiency ishighest in the effectively central region of the diagram wherein thehorizontal axis is a corrected mass flowrate QA, and the vertical axisis a pressure ratio π.

The corrected mass flow QA and pressure ratio π are defined by thefollowing equations (26), (27). $\begin{matrix}{{QA} = {Q \cdot \frac{T}{P} \cdot \frac{1}{2}}} & (26)\end{matrix}$

where,

Q=volumetric flowrate of exhaust gas driving the exhaust gas turbine(m³/sec),

T=absolute temperature of exhaust gas at turbine inlet (° K), and

P=absolute pressure of exhaust gas at turbine inlet (Pa).$\begin{matrix}{\pi = \frac{P1}{P0}} & (27)\end{matrix}$

where,

P1=outlet pressure of compressor (Pa)=manifold pressure Pm, and

P0=inlet pressure of compressor (Pa)=atmospheric pressure Pa.

Expressing this characteristic as a graph wherein the horizontal axis isan exhaust gas amount and the vertical axis is an EGR amount, it may bedivided into essentially three regions depending only on the exhaust gasamount, as shown in FIG. 101. Of these, the region where the chargingefficiency increases together with increase in the exhaust gas amount isthe small exhaust gas amount region, the region where the chargingefficiency decreases together with increase in the exhaust gas amount isthe large exhaust gas amount region, and the region with littlevariation of charging efficiency is the intermediate region. Theseregions may also be classified based on the charging efficiency itself,but as the calculation of charging efficiency is complex, the exhaustgas amount is used instead of the charging efficiency for convenience.

As shown in FIG. 101, these regions are hardly affected by the EGRamount, so the advance correction gain TGKVNTO when the variable nozzle53 is opened and the advance correction gain TGKVNTC when it is closed,are set using only the exhaust gas amount as a parameter.

The maps of FIG. 62 and FIG. 63 are set based on the above analysis.

As shown in these maps, in the small exhaust gas amount region, theadvance correction gain TGKVNTC is larger than the advance correctiongain TGKVNTO, and in the large exhaust gas amount region, the advancecorrection gain TGKVNTC is smaller than the advance correction gainTGKVNTO.

In a step S331, an estimated opening rate Cavnt is calculated by thefollowing equation (28) using the target opening rate Rvnt and theadvance correction time constant equivalent value Tcvnt

Cavnt=Rvnt·Tcvnt+Cavnt _(n−1)·(1−Tcvnt)  (28)

where,

Cavnt_(n−1)-Cavnt calculated on the immediately preceding occasion thesubroutine was executed.

In the maps of FIG. 62 and FIG. 63, in the small exhaust gas amountregion, the correction gains TGKVNTO, TGKVNTC are set so that they areeffectively constant values. Likewise, in the large exhaust gas amountregion, they are set so that they are effectively constant values.

As the gas flow lag becomes larger, the smaller the exhaust gas amount,it is desirable to make a setting such that the correction gainsTGKVNTO, TGKVNTC increase the smaller the real exhaust gas amountequivalent value Tqexhd so as to improve control response.

Conversely, in the large exhaust gas amount region, it is desirable tomake the correction gains TGKVNTO, TGKVNTC smaller, the larger the realexhaust gas amount equivalent value Tqexhd so as to improve controlresponse.

However, to perform this setting, it is difficult to make the correctiongains TGKVNTO, TGKVNTC match the actual control, so according to thisembodiment, the correction gains TGKVNTO; TGKVNTC are respectively madefixed values in the small exhaust gas amount region and the largeexhaust gas amount region, considering the stability of control.

In the small exhaust gas amount region, when the variable nozzle 53 isdriven in the closing direction as shown in FIG. 63, the value of thegain is set larger than in the case where it is driven in the openingdirection, as shown in FIG. 62. This is because the gas flow lag islarger when the variable nozzle 53 is closing than when it is opening.

The maps of FIG. 64 and FIG. 65 which define the time constantequivalent values TTCVNTO, TTCVNTC give a larger value, the larger thereal exhaust gas amount equivalent value Tqexh.

Here, the time constant equivalent value is an inverse of the timeconstant that represents the operation speed of the actuator (54).Hence, the time constant becomes smaller, as the real exhaust gas amountequivalent value Tqexh becomes larger.

Further, the time constant equivalent value TTCVNTO when the variablenozzle 53 is opening takes a larger value than the time constantequivalent value TTCVNTC when the variable nozzle 53 is closing, for thesame real exhaust gas amount equivalent value Tqexh, i.e., the timeconstant when the variable nozzle 53 is opening, is less than the timeconstant when it is closing.

In a following step S332, an open loop control amount Avnt_f of theopening rate of the variable nozzle 53 is calculated by the followingequation (29) from an opening prediction value Cavnt and a targetopening rate Rvnt.

 Avnt _(—) f=Gkvnt·Rvnt−(Gkvnt−1)·Cavnt _(n−1)  (29)

The calculation of the steps S331, S332 is similar to the calculation ofthe steps S24, S25 of the routine of FIG. 6.

Although equation (29) is an advance processing equation, application ofadvance processing by this equation is limited to the case where theadvance correction gain Gkvnt is larger than 1.0.

In the maps of FIG. 62 and FIG. 63, in the large exhaust gas amountregion, the advance correction gains TGKVNTO, TGKVNTC are set to apositive value less than 1.0. In this case, the advance processingequation (29) effectively becomes a delay processing equation. Ingeneral, among delay processing equations, first order delay equationsare well known, but the application of equation (29) to delay processingis not common.

FIG. 103 shows simulated results for how the open loop control amountAvnt_f of the target opening rate varies when equation (29) is used fordelay processing, by setting the advance correction gain Gkvnt to 0.5and the time constant equivalent value Tcvnt of the advance correctionto 0.1.

Referring to FIG. 103, when equation (29) is applied, there is adifference from the case where the ordinary first order delay equationis applied, in that the open loop control amount Avnt_f starts stepwiseat the timing when the target opening rate Rvnt changes in a stepwisefashion. This means that the response of equation (29) is higher thanthat of the ordinary first delay processing equation. For comparison,the simulation result for the open loop control amount Avnt_f whenequation (29) is used for advance processing is shown in FIG. 102, wherethe advance correction gain Gkvnt is set to 2.0 and the time constantequivalent value Tcvnt is set to 0.1.

In a last step S333, a delay processing value Rvnte of the targetopening rate Rvnt is calculated from the following equation (30).

Rvnte=Rvnt·TCVNT#−(TCVNT#−1)·Rvnte _(n−1)  (30)

where,

TCVNT#=time constant equivalent value representing the response delay ofthe pressure actuator 54, and

Rvnte⁻¹=Rvnte calculated on the immediately preceding occasion theroutine was executed.

The delay processing value Rvnte is a value taking account of theresponse delay of the pressure actuator 54, and corresponds to the realopening rate. In this regard, the delay processing value Rvnte of theopening rate Rvnt will be referred to as the real opening rate.

The response delay of the pressure actuator 54 is identical whether thevariable nozzle 53 is closing or whether it is opening. Therefore, thetime constant equivalent value TCVNT# is a constant. The real openingrate Rvnte is used for calculating a PI gain opening rate correctioncoefficient Gkvavnt and an opening rate reflection coefficient Gkvntlavdescribed later.

After the controller 41 calculates the opening prediction value Cavnt,open loop control amount Avnt_f and the real opening rate Rvnte by theroutine of FIG. 60 in this way, a feedback correction amount Avnt_fb ofthe opening rate and a learning value Ravir related to the feedbackcorrection amount Avnt_fb are calculated in a step S245 of FIG. 38. Thiscalculation is performed by a subroutine shown in FIG. 66.

Referring to FIG. 66, in a step S601, the controller 41 first sets afeedback control permission flag FVNFB of the opening rate of thevariable nozzle 53 by a subroutine shown in FIG. 67.

Referring to FIG. 67, in a step S341, it is determined whether or notthe running condition of the diesel engine 1 corresponds to a feedbackcontrol region of the opening rate of the variable nozzle 53 referringto a map prestored in the controller 41 whereof the contents are shownin FIG. 68.

In this map, the feedback control region is all running regionsexcluding low load and low rotation speed regions of the diesel engine1. The reason why feedback control of the opening rate of the variablenozzle 53 is not performed under low load and at low rotation speed isbecause the intake fresh air amount hardly varies relative to variationof the opening rate of the variable nozzle 53 in this region, i.e., thesensitivity of the intake fresh air amount relative to variation of theopening rate is small. Therefore, in this region, not performingfeedback control of the opening rate leads to stable control of theintake fresh air amount of the diesel engine 1 and the superchargingpressure of the turbocharger 50. A hysteresis region is provided asshown in the figure between the feedback control region and non-feedbackcontrol region.

In the step S341, when the running condition of the diesel engine 1 isin the feedback control region, the subroutine determines whether or notfeedback control permission conditions are satisfied for the openingrate of the variable nozzle 53, from a step S342 to a step S344.

First, in the step S342 it is determined whether or not the target EGRrate Megr is less than a predetermined value KVNFBMEGR#.

In the step S343 it is determined whether or not an immediatelypreceding value FCLPVNDTY_(n−1) of a command opening rate clamp flagFCLPVNDTY, described later, is zero showing a clamp state.

In the step S344, it is determined whether or not an air flow meterfault determining flag FDGMAF is zero, showing the normal state. The airflow meter determining flag FDGMAF is set to be one by a routine notdescribed here when the air flow meter 39 does not operate correctly.

When the determination results of all of the steps S342-S244 areaffirmative, the subroutine sets the feedback control permission flagFVNFB of the opening rate of the variable nozzle 53 to one in a stepS345 and the subroutine is terminated. When the determination result ofany of the steps S342-S344 is negative, the subroutine resets thefeedback control permission flag FVNFB of the opening rate of thevariable nozzle 53 to zero in a step S356, and the subroutine isterminated.

According to the step S342, in the EGR recirculation region, thefeedback control permission flag FVNB is reset to zero, and opening ratefeedback control of the variable nozzle 53 is not performed. This is dueto the following reason. In the EGR recirculation region, the opening ofthe EGR valve 6 is feedback controlled. Therefore, feedback control ofthe opening rate of the variable nozzle 53 in this region causesinterference between the two feedback controls, and the value of theopening rate tends to fluctuate.

According to the step S343, when the command opening rate is clamped,feedback control of the opening rate of the variable nozzle 53 is notperformed. Clamping of the command opening rate is performed when theopening rate has converged, as described hereafter. In this case, thereis no need to perform feedback control of the opening rate of thevariable nozzle 53.

According to the step S344 feedback control of the opening rate of thevariable nozzle 53 is not performed when the air flow meter 39 has afault. This is in order to provide a fail-safe mechanism.

After setting the feedback control permission flag FVNFB, the controller41 sets a feedback gain in the step S602 of FIG. 66. This processing isperformed by a subroutine shown in FIG. 69.

First, in a step S351, the delay processing value tQacd of the targetintake fresh air amount, cylinder intake fresh air amount Qac, realexhaust gas amount equivalent value Tqexhd and real opening rate Rvnteare read.

In a next step S352, it is determined whether or not the feedbackcontrol permission flag FVNFB is one.

When the feedback control permission flag FVNFB is not one i.e., whenfeedback control of the variable nozzle 53 is not performed, a controlerror Eqac is set to zero in a step S353. When the feedback controlpermission flag FVNFB is one, i.e., when feedback control of thevariable nozzle 53 is performed, a value obtained by subtracting thedelay processing value tQacd from the cylinder intake fresh air amountQac is set to the control error Eqac in a step S354.

In normal feedback control, the target intake fresh air amount tQac is atarget value set according to the running conditions, but in thisinvention, as a response time and a response time constant are the mainobjects of control, the target intake air amount delay processing valuetQacd is taken as the target value of feedback control. The differencebetween the cylinder intake fresh air amount Qac and target value tQacdis considered as the control error Eqac.

After the step S353 or the step S354, the subroutine calculates aproportional gain basic value Gkvntp0 and integral gain basic valueGkvnti0 by looking up maps whereof the contents are shown in FIG. 70 andFIG. 71 which are prestored in the controller 41, from the control errorEqac. In these maps, an insensitive region is provided around the valuezero of Eqac so that the feedback control does not fluctuate in thevicinity of the target value.

In a following step S356, an exhaust gas amount correction coefficientGkvqexh of the proportional gain and integral gain is calculated bylooking up a map whereof the contents are shown in FIG. 72 which isprestored in the controller 41 from the real exhaust gas amountequivalent value Tqexhd.

In a next step S357, an opening rate correction coefficient Gkvavnt iscalculated referring to a map whereof the contents are shown in FIG. 73which is prestored in the controller 41 from the real opening rateRvnte.

In a next step S358, the proportional gain Gkvntp and integral gainGkvnti are calculated by the following equations (31) from these basicvalues and correction coefficients.

Gkvntp=Gkvntp 0 ·Gkvqexh·Gkvavnt  (31)

Gkvnti=Gkvnti 0 ·Gkvqexh·Gkvavnt

The exhaust gas amount correction coefficient Gkvqexh shown in the mapof FIG. 72 takes a smaller value the larger the real exhaust gas amountequivalent value Tqexhd. For an identical opening rate of the variablenozzle 53, the variation of supercharging pressure increases the largerthe exhaust gas amount, therefore it is easier to make the superchargingpressure approach the target value. In other words, at a low exhaust gasamount, the variation of supercharging pressure relative to thevariation of opening rate is sluggish. Hence, to make the superchargingpressure at a low exhaust gas amount converge to the target valueearlier, the exhaust gas amount correction coefficient Gkvqexh is set tobe larger as the real exhaust gas amount equivalent value Tqexhddecreases

The opening rate correction coefficient Gkvavnt shown in the map of FIG.73 takes a smaller value the smaller the real opening rate Rvnte. Whenthe opening of the variable nozzle 53 is small, the superchargingpressure reacts more sensitively to a variation in the opening rate thanwhen the opening is large. To average out the response, the opening ratecorrection coefficient Gkvavnt is set to take a smaller value thesmaller the real opening rate Rvnte.

In this way, after the feedback correction coefficients are set by thesubroutine of FIG. 69, the controller 41 calculates the feedbackcorrection amount Avnt_fb using a subroutine shown in FIG. 74 in a stepS603 of FIG. 66.

Referring to FIG. 74, the controller 41 first reads the intake fresh airamount Qac and delay processing value tQacd of the target intake freshair amount in a step S361.

In a step S362, it is determined whether or not a feedback controlpermission flag FVNFB is one.

When the feedback control permission flag FVNFB is not one, i.e., whenfeedback control of the variable nozzle 53 is not performed, the controlerror Eqac is set to zero in a step S363. When the feedback controlpermission flag FVNFB is one, i.e. when feedback control of the variablenozzle 53 is performed, a value obtained by subtracting the delayprocessing value tQacd from the cylinder intake fresh air amount Qac isset to the control error Eqac in a step S354. The processing of thesteps S362 to S364 is identical to the processing of the steps S352 toS354 of FIG. 69.

In a step S365, a proportional correction value Ravfbp is calculatedfrom the following equation (32).

Ravfbp=Gkvntp·Eqac  (32)

In a next step S366 an integral correction value Ravfbi is calculated bythe following equation (33).

Ravfbi=Gkvnti·Eqac+Ravfbi _(n−1) −dTravir  (33)

where,

Ravfbi_(n−1)=Ravfbi calculated on immediately preceding occasion thesubroutine was executed, and

dTravir=variation amount of the learning value Ravir calculated by asubroutine of FIG. 77 described hereafter.

In a next step S367, the feedback amount Avnt_fb of the opening rate ofthe variable nozzle 53 is calculated by summing the proportionalcorrection amount Ravfbp and integral correction amount Ravfbi.

Apart from the third term on the right-hand side of equation (33) usedin the step S366, this equation corresponds to the calculation equationin ordinary learning control. According to this invention, the variationamount dTravir of the learning value Ravir is subtracted from theintegral correction value Ravfbi obtained in the calculation equation ofthe prior art learning control. The calculation of the learning valueRavir and its variation amount dTravlr will be described later, but theinterval of the calculation of both the integral correction amountRavfbi and learning value Ravir is ten milliseconds.

After the controller 41 calculates the feedback correction amountAvnt_fb by the subroutine of FIG. 74 in this way, a learning permissionflag FVLNR is calculated in a step S604 of FIG. 66. The learningpermission flag FVLNR is a flag which determines whether or not learningof the integral correction amount Ravfbi is permitted. This calculationis performed by a subroutine shown in FIG. 75.

Referring to FIG. 75, the controller 41 first reads the target EGR rateMegr, atmospheric pressure Pa, cooling water temperature Tw, controlerror Eqac and delay processing value tQacd of the target intake freshair amount in a step S371.

In following steps S372-S379, it is determined whether or not the enginerunning conditions are suitable for learning of the integral correctionamount Ravfbi from the parameters which were read.

In the step S372, it is determined whether or not the running conditionof the diesel engine 1 corresponds to a learning region specified in amap whereof the contents are shown in FIG. 76 which is prestored in thecontroller 41, from the rotation speed Ne of the diesel engine 1 and thetarget fuel injection amount Qsol which represents the load of thediesel engine 1. The map of FIG. 76 is simplified, but in practice, theregion which is the supercharging pressure feedback control region andwhere the learning sensitivity is good, i.e., the region where thevariation of the intake fresh air amount is large relative to thevariation of opening rate of the variable nozzle 53 is set as thelearning region.

In a step S373, it is determined whether or not the current value of thelearning permission flag FVLNR is one.

In a step S374, it is determined whether or not the target EGR rate Megris less than a predetermined rate KVNLRMEGR#. The predetermined rateKVNLRMEGR# is a value for determining whether or not exhaust gasrecirculation is to be performed, and when the target EGR rate Megr isless than the predetermined value KVNLRMEGR#, exhaust gas recirculationis effectively not performed.

In a step S375, it is determined whether or not the atmospheric pressurePa is higher than a predetermined pressure KVLNRPA#. The predeterminedpressure KVLNRPA# is a pressure corresponding to running on high ground,and when the condition of the step S375 is satisfied, it shows that thevehicle is not running on high ground.

In a step S376, it is determined whether or not the cooling watertemperature Tw is higher than a predetermined temperature KVNLRTW#. Thepredetermined temperature KVNLRTW# is a value which determines whetheror not warm-up of the diesel engine 1 is complete, and when the coolingwater temperature Tw is higher than the predetermined temperatureKVNLRTW#, it is considered that warm-up is complete.

In a step S377, it is determined whether or not the absolute value ofthe ratio of the control error Eqac and the delay processing value tQacdof the target fresh air amount is less than a predetermined valueKVNLREQA#. When the absolute value of this ratio is large, it signifiesthat the control of supercharging pressure is subject to the effect ofexternal disturbance. The predetermined value KVNLREQA# is a referencevalue for performing this determination, and when the absolute value ofthis ratio is less than the predetermined value KVNLREQA#, it isconsidered that there is no effect due to external disturbance. Thereason why the ratio of the delay processing value tQacd of the targetintake fresh air amount and the control error Eqac is taken as thedetermining parameter, is in order to maintain the ratio of the controlerror relative to the target value constant even if the target valuevaries. However, to simplify the calculation, it is also possible todetermine the presence or absence of external disturbance by comparingthe absolute value of the control error Eqac with a predetermined value.

In a step S378, it is determined whether or not the overboostdetermining flag FOVBST and suppression release flag FCLROB are bothzero. If these flags are zero, it signifies that the overboostsuppression control is not performed.

In a step S379, it is determined whether or not an air flow meter faultdetermining flag FDGMAF is zero, showing the normal state.

When all the conditions of the steps S372-S379 are satisfied, thelearning permission flag FVLNR is set to one in a step S380 so as topermit learning of the integral correction amount Ravfbi. When any ofthe conditions of the steps S372-S379 is not satisfied, the learningpermission flag FVLNR is reset to zero in a step S381 so as to prohibitlearning of the integral correction amount Ravfbi.

In this way, after setting the learning permission flag FVLNR, thecontroller 41 calculates the learning value Ravlr in a step S605 of FIG.66. This calculation is performed by the subroutine of FIG. 77.

Referring to FIG. 77, first in a step S391, the controller 41 sets theimmediately preceding value Ravlr_(n−1) equal to the learning valueRavlr stored in a non-volatile memory in the controller 41.

In a next step S392, it is determined whether or not the learningpermission flag FVLNR is one. When the learning permission flag FVLNR isone, learning of the integral correction amount Ravfbi is performed insteps S393-S396. On the other hand, when the learning permission flagFVLNR is not one, a processing outside the learning region is performedin steps S397-S400.

Here, learning means that the integral correction amount Ravfbi islearned, the learning value Ravlr for opening rate control is calculatedbased on a learning initial value Ravlr0 and immediately preceding valueRavlr_(n−1) of the learning value Ravlr, and the immediately precedingvalue Ravlr_(n−1) stored in the non-volatile memory is newly updated tothe calculated value.

Processing outside the learning region means that the learning valueRavlr for opening rate control is calculated by multiplying theimmediately preceding value Ravlr_(n−1) by a predetermined coefficient.In this case, the value stored in the non-volatile memory is notupdated.

The specific details of learning will now be described referring to thesteps S393-S396.

In the step S393, the learning initial value Ravlr0 is set to equal tothe integral correction amount Ravfbi of the opening rate of thevariable nozzle 53.

In the next step S394, a learning rate Kfntlrn is calculated by lookingup a map whereof the contents are shown in FIG. 78 which is prestored inthe controller 41, based on the engine rotation speed Ne and the targetfuel injection amount Qsol which represents the engine load. In thismap, the learning rate Kvntlrn is increased, the larger the enginerotation speed No and the target fuel injection amount Qsol However,when it increases, the variation of the intake fresh air amount relativeto variation of opening rate of the variable nozzle 53 becomes moresensitive. Specifically, when the engine rotation speed Ne and targetfuel injection amount Qsol are large, convergence to the target value ofthe supercharging pressure or intake fresh air amount is advanced byincreasing the learning proportion of the feedback correction amount.For this purpose, the learning rate Kvntlrn is set large, the larger theengine rotation speed Ne and target fuel injection amount Qsol. However,the maximum value of the learning rate Kvntlrn is one.

In the next step S395, the learning initial value Ravlr0 and immediatelypreceding value Ravlr_(n−1) of the learning value Ravlr are weighted bythe following equation (34) to calculate the learning value Ravlr.

Ravir=Kvntlrn·Ravlr 0+(1−Kvntlrn)·Ravlr _(n−1)  (34)

According to equation (34), when the learning rate Kvntlrn is themaximum value of one, on the next occasion the control of the openingrate is performed, the total amount of the integral correction amountRavfbi is used as the learning value Ravlr. When the learning rateKvntlrn is less than 1, part of the integral correction amount Ravfbi isused as the learning value Ravlr on the next occasion control of theopening rate is performed.

In the next step S396, the calculated learning value Ravlr is stored inthe non-volatile memory. This value is used as the immediately precedingvalue Ravlr_(n−1) on the next occasion when the routine is performed.

Next, specific details of processing outside the learning region will bedescribed referring to the steps S397 to S400.

In the step S397, the initial learning value Ravlr0 is set equal to theimmediately preceding value Ravlr⁻¹.

In the next step S398, the running region reflection coefficientGkvntlnq of the learning value is calculated, referring to a map whereofthe contents are shown in FIG. 79 which is prestored in the controller41, based on the engine rotation speed Ne and target fuel injectionamount Qsol.

In the next step S399, the opening rate reflection coefficient Gkvntlavis calculated, referring to a map whereof the contents are shown in FIG.80 which is prestored in the controller 41, based on the real openingrate Rvnte.

In the next step S400, the learning value Ravir for the opening ratecontrol is calculated by the following equation (35).

Ravir=Ravlr 0·Gikvnt In q·Gkvnilav  (35)

The equation (35) is applied to have the learning value reflected insupercharging pressure control outside the learning region. The learningvalue Ravlr obtained is applied to learning control of the opening ratedescribed hereafter, but the value stored in the non-volatile memory isnot updated.

Referring to the map of FIG. 79, the running region reflectioncoefficient Gkvntlnq is one when the engine rotation speed Ne and targetfuel injection amount Qsol are in the learning region, and becomesmaller, the further away from the learning region. In a region which islargely removed from the running region where the learning value Ravlris learned, if opening rate control is performed applying the samelearning value Ravlr as in the learning region, the error becomes toolarge, and the possibility of causing overboost increases. To preventthis overboost, the map characteristics are set so that the runningregion reflection coefficient Gkvntlnq become smaller the further awayfrom the learning region.

In the map of FIG. 80, an opening rate reflection coefficient Gkvntlavis set to be small in a region where the real opening rate Rvnte issmall. The variation of intake fresh air amount relative to thevariation of opening rate, is larger the smaller the opening rate. As aresult, in a region where the opening rate is small, when the learningvalue is largely reflected in supercharging pressure control, there is ahigh possibility of causing overboost. To prevent this overboost, in theregion where the opening rate is small, the map characteristics are setso that the opening rate reflection coefficient Gkvntlav becomes smallerin the region where the opening rate is small.

After performing the processing of the steps S392-S396 or the steps S397to S400 in this way, the controller 41 calculates the difference betweenthe learning value Ravlr and immediately preceding value Ravlr_(n−1)stored in the non-volatile memory in a step S401, as the variationamount dTravlr of the learning value. This variation amount dTravlr is avalue used in the calculation of the step S365 of FIG. 74 describedearlier. As can be seen from FIG. 66, the subroutine of FIG. 74 isperformed before the subroutine of FIG. 77 which calculates thevariation amount dTravlr. Therefore, the variation amount dTravlrcalculated in the subroutine of FIG. 77 is used on the next occasionwhen the subroutine of FIG. 74 is performed.

When the subroutine of FIG. 77 terminates, the subroutine of FIG. 66also terminates.

Now, referring again to the main routine of FIG. 38, after calculatingthe feedback correction amount Avnt_fband the variation amount dTravlrof the learning value by the subroutine of FIG. 66 in the step S245, thecontroller 41 calculates a final command opening rate Trvnt sand acommand opening rate linearization processing value Ratdty in afollowing step S246. This calculation is performed by subroutines ofFIG. 81 and FIG. 82

Referring to FIG. 81, firstly in a step S411, the controller 41 readsthe open loop control amount Avnt_f of the command opening rate, thefeedback correction amount Avnt_fb of the command opening rate and thelearning value Ravlr.

In a next step S412, the command opening rate Avnt is calculated bysumming these values.

In a next step S413, to compensate the response delay of the pressureactuator 54, advance processing is performed on the command opening rateAvnt using a subroutine of FIG. 82. The pressure actuator 54 comprisesthe diaphragm actuator 59 which is operated by the supply pressure ofthe pressure control valve 56, so some time is required from when a dutysignal is input to the pressure control valve 56 to when the diaphragmactuator 59 actually operates corresponding to the duty signal. Theprocessing of the step S413 is processing to compensate this responsedelay. If the variable nozzle 53 is operated by a step motor instead ofthe pressure actuator 54, this step is unnecessary.

Referring to FIG. 82, the controller 41 first reads the command openingrate Avnt in a step S421.

In a next step S422, it is determined whether or not the absolute valueof the difference between the immediately preceding value Avnt_(n−1) ofthe command opening rate read on the immediately preceding occasion thesubroutine was executed and the command opening rate Avnt read on thepresent occasion, is smaller than a predetermined value EPSDTY#.

When the determination result of the step S422 is negative, it showsthat the command opening rate Avnt is varying. In this case, afterresetting a clamp flag FCLPVNDTY of the command opening rate to zero ina step S423, the routine proceeds to a step S424 and subsequent steps.

On the other hand, when the determination result of the step S422 isaffirmative, it shows that the command opening rate Avnt is not varying.In this case, after setting the clamp flag FCLPVNDTY of the commandopening rate to one in a step S429, the routine proceeds to a step S430and subsequent steps.

In the step S345 of FIG. 67 described above, the clamp flag FCLPVNDTY isused to determine whether or not feedback control of the opening rate ispermitted. The clamp flag FCLPVNDTY varies from zero to one when thevariation of the command opening rate Avnt is complete. In this case, asit is determined that feedback control of the opening rate is no longernecessary, the clamp flag FCLPVNDTY is set to one.

In the step S424, the controller 41 compares the command opening rateAvnt and the immediately preceding value Avnt_(n−1) of the commandopening rate. When Avnt is larger than Avnt_(n−1), it shows that theactuator 54 is opening the variable nozzle 53. In this case, thesubroutine sets an actuator advance correction gain Gkact equal to aconstant value GKVACTP# for opening in a step S425, sets a time constantequivalent value Tcact for actuator advance correction equal to aconstant value TCVACTP# for opening in a step S426, and proceeds to astep S432.

On the other hand, when Avnt is not larger than Avnt_(n−1), the actuator54 is closing the variable nozzle 53. In this case, the subroutine setsthe actuator advance correction gain Gkact equal to a constant valueGKVACTN# for closing in a step S427, sets the time constant equivalentvalue Tcact for actuator advance correction equal to a constant valueTCVACTN# for closing in a step S428, and then proceeds to the step S432.

Here, GKVACTP#<GKVACTN# and TCVACTP#<TCVACTN#. The operation whereby thepressure actuator 54 closes the variable nozzle 53 is performed inopposition to the exhaust gas pressure. Therefore, the actuator advancecorrection gain Gkact in this case must be set larger than when thevariable nozzle 53 is opened. Conversely, the time constant of theactuator advance correction when the pressure actuator 54 closes thevariable nozzle 53 must be set smaller than when the variable nozzle 53is opened. As the time constant equivalent value Tcact is the inverse ofthe time constant, the value when the pressure actuator 54 closes thevariable nozzle 53 must be set larger than the value when the variablenozzle 53 is opened.

When the clamp flag FCLPVNDTY of the command opening rate is set to onein the step S429, in the subsequent step S430, the controller 41 setsthe actuator advance correction gain Gkact equal to a value Gkact_(n−1)set on the immediately preceding occasion the subroutine was executed.

In a subsequent step S431, the time constant equivalent value Tcact isset equal to a value Tcact_(n−1) set on the immediately precedingoccasion the subroutine was executed, and the routine proceeds to thestep S432.

In the step S432, the opening prediction value Cvact is calculated bythe following equation (36) using the time constant equivalent valueTcact and command opening rate Avnt.

Cvact=Avnt·Tcact+Cvact _(n−1)·(1−Tcact)  (36)

where,

Cvact_(n−1)=opening prediction value Cvact calculated on the immediatelypreceding occasion the subroutine was executed.

Further, in a next step S433, the final command opening rate Trvnt iscalculated by the following equation (37) using the opening predictionvalue Cvact and command opening rate Avnt.

Trvnt=Gkact·Avnt−(Gkact−1)·Cvact_(n−1)  (37)

The significance of the processing of the steps S432 and S433 isidentical to that of the calculation of the intermediate value Rqec andtarget EGR amount Tqec in the steps S24 and S25 of FIG. 6.

Hence, in the subroutine of FIG. 82, advance processing is performedtaking account only of the response delay of the pressure actuator 54.The advance correction related to the gas flow lag dependent on theintake air, exhaust gas flowrate and turbo lag is performed by thesubroutine of FIG. 60 described above.

After calculating the final command opening rate Ttvnt in this way, thecontroller 41 calculates a command opening rate linearization processingvalue Ratdty in a step S414 of FIG. 81. The command opening ratelinearization processing value Ratdty is calculated by looking up a mapwhereof the contents are shown in FIG. 83 which is prestored in thecontroller 41, based on the final command opening rate Trvnt.

This linearization processing is required when the opening rate oropening surface area of the variable nozzle 53, and the duty signaloutput by the controller 41 through the pressure control valve 56, havea nonlinear correspondence.

Returning now to the main routine of FIG. 38, after the controller 41calculates the command opening rate linearization processing valueRatdty, a duty value Dtyvnt of the duty signal output to the pressurecontrol valve 56 is calculated in a step S247. This calculation isperformed using the subroutine of FIG. 84.

Referring to FIG. 84, in a step S441, the controller 41 reads the enginerotation speed Ne, target fuel injection amount Qsol, linearizationprocessing value Ratdty of the command opening rate, advance correctiontime constant inverse value Tcvnt and cooling water temperature Tw ofthe diesel engine 1.

In a step S442, duty signal variation flags are set using the subroutineshown in FIG. 85.

Referring to FIG. 85, the controller 41 first reads the command openingrate Avnt and the advance correction time constant inverse value Tcvntin a step S461.

In a next step S462, a command opening rate prediction value Adfyvnt iscalculated by the following equation (38).

Adlyvnt=Avnt·Tcvnt+Adlyvnt _(n−1)·(1−Tcvnt)  (38)

where,

Adlyvnt_(n−1)=value of Adlyvnt calculated on the immediately precedingoccasion the subroutine was executed.

Here, the relation between the command opening rate Avnt and the commandopening rate prediction value Adlyvnt corresponds to the relationbetween the target opening rate Rvnt and the opening prediction valueCavnt.

In a following step S463, the command opening rate prediction valueAdlyvnt is compared with a command opening rate prediction valueAdlyvnt_(n−m) calculated by the subroutine executed M times ago.

When Adlyvnt≧Adlyvnt_(n−M), the command opening rate is increasing orconstant. In this case, the subroutine sets an operation direction flagfvnt to one in a step S464, and proceeds to a step S466.

In the step S466, it is determined whether or not Adlyvnt=Adlyvnt_(n−M).When Adlyvnt=Adlyvnt_(n−M) in a step S467, a duty hold flag fvnt2 is setto one, and the subroutine is terminated.

When Adlyvnt=Adlyvnt_(n−M) is not satisfied, the routine proceeds to astep S468.

When Adlyvnt<Adlyvnt_(n−M) in the step S463, it shows that the commandopening rate is decreasing. In this case, the subroutine resets theoperation direction flag fnvt to zero in a step S465, and the routineproceeds to the step S468.

In the step S468, the duty hold flag fvnt2 is reset to zero, and thesubroutine is terminated.

Thus, after setting the two flags fvnt and fvnt2, the controller 41reads a duty value temperature correction amount Dty_t in a step S443 ofFIG. 84. The duty value temperature correction amount Dty_t iscalculated by a subroutine of FIG. 86 performed independently insynchronism with the REF signal.

Referring to FIG. 86, in a step S471, the controller 41 first reads theengine rotation speed Ne, target fuel injection amount Qsol and coolingwater temperature Tw.

In a step S472, a basic exhaust gas temperature Texhb is calculated fromthe engine rotation speed Ne and target fuel injection amount Qsol bylooking up a map shown in FIG. 87 previously stored in the memory of thecontroller 41. The basic exhaust gas temperature Texhb is the exhaustgas temperature after the diesel engine 1 has completed warming up.

In a next step S473, a water temperature correction coefficient Ktexh_twis calculated by looking up a map shown in FIG. 88 stored in thecontroller 41, based on the cooling water temperature Tw.

In a step S474, an exhaust gas temperature Texhi is calculated bymultiplying the basic exhaust gas temperature Texhb by the watertemperature correction coefficient Ktexh_tw.

In a next step S475, a real exhaust gas temperature Texhdly iscalculated by adding a first order processing delay to the exhaust gastemperature Texhi by the following equation (39). This value is a valuewhich takes account of the delay due to the heat inertia in thevariation of exhaust gas temperature.

Texhdly=Texhi·KEXH#+Texhdly _(n−1)·(1−KEXH#)  (39)

where,

KEXH#=constant, and

Texhdly_(n−1)=Texhdly calculated on the immediately preceding occasionwhen the subroutine was executed.

In a following step S476, a difference dtexh of the basic exhaust gastemperature Texhb and this real exhaust gas temperature Texhdly iscalculated.

In a last step S477, the duty value temperature correction amount Dty_tis calculated by looking up a map shown in FIG. 89 previously stored inthe memory of the controller 41, based on the difference dtexh. Themeaning of the processing of the steps S476 and S477 will be describedin detail later.

After the end of the subroutine, the controller 41 returns to thesubroutine of FIG. 84 and performs processing after the step S444. StepsS444-S449 are steps which add hysteresis processing to the duty value.

Describing this hysteresis processing with reference to FIG. 95, whenthe linearization processing value Ratdty of the command opening rateAvnt is increasing, the duty value is made to vary according to astraight line which joins a command signal Duty_l_p when the variablenozzle 53 is fully open, and a command signal Duty_h_p when the variablenozzle 53 is fully closed. On the other hand, when the linearizationprocessing value Ratdty is decreasing, the duty value is made to varyaccording to a straight line which connects a command signal Duty_l_nwhen the variable nozzle 53 is fully open, and a command signal Duty_h_nwhen the variable nozzle 53 is fully closed. In the drawing, two linesintersect in the region where the variable nozzle 53 is nearly closed,but this region is a region which is not used in actual control of thepressure control valve 56. These characteristics are set assuming thatthe diesel engine 1 has completely warmed up. When the real exhaust gastemperature Texhdly is low, the pressure actuator 54 has thecharacteristic of opening the variable nozzle 53 larger for the sameduty value, as shown in FIG. 90. Hence, it is necessary to apply thetemperature correction amount Dty_tcalculated in the steps S476, S477 ofFIG. 86, to compensate the difference in the characteristic of thepressure actuator 54 due to the exhaust gas temperature.

Now, the controller 41 determines the operation direction flag fvnt inthe step S444. When the operation direction flag fvnt is one, i.e., whenthe command opening rate Avnt is increasing or constant, the processingof steps S445, S446 is performed. In the step S445, a duty value Duty_hwhen the variable nozzle 53 is fully closed, is calculated based on thetarget fuel injection amount Qsol by looking up a Duty_h_p map shown inFIG. 91.

In the following step S446, a duty value Duty_l when the variable nozzle53 is fully open, is calculated by looking up a Duty_l_p map shown inFIG. 92. After this processing, the subroutine proceeds to a step S449.

When the operation direction flag fvnt is zero in the step S444, i.e.,when the command opening rate Avnt is decreasing, the processing ofsteps S447, S448 is performed. In the step S447, the duty value Duty_hwhen the variable nozzle 53 is fully closed, is calculated based on thetarget fuel injection amount Qsol by looking up a Duty_h_n map shown inFIG. 93. In the following step S448, the duty value Duty_l when thevariable nozzle 53 is fully open, is calculated based on the target fuelinjection amount Qsol by looking up a Duty_l_n map shown in FIG. 94.

After this processing, the subroutine proceeds to a step S449.

In the step S449, a command duty basic value Dty_h is calculated byperforming linear interpolation processing by the following equation(40) using the duty values Duty_h, Duty_l found by the above processing,the linearization processing value Ratdty of the command opening rateAvnt, and the temperature correction amount Dty_t.

Dty _(—) h=(Duty_(—) h−Duty_(—) l)·Ratdty+Duty_(—) l+Dty _(—) t  (40)

By changing the straight line used for linear interpolation processingin the case where the command opening rate Avnt, is decreasing, and thecase where it is not, the command duty basic value Dty_h is madesmaller, for the same linearization processing value Ratdty, in the casewhere the command opening rate Avnt is decreasing than in other cases.

In a next step S450, the duty hold flag fnt2 is determined. When theduty hold flag fvnt2 is one, i.e., the command opening rate predictionvalue Adlyvnt is not changing, a command duty value Dtyv is set equal tothe duty value Dtyvnt_(n−1) calculated on the immediately precedingoccasion the subroutine was executed, in a step S451. The duty valueDtyvnt_(n−1) will be described in detail later.

When the duty hold flag fvnt2 is zero, i.e., when the command openingrate prediction value Adlyvnt is changing, in a step S452, the commandduty value Dtyv is set equal to the command duty basic value Dty_hcalculated in the step S449.

Thus, after determining the command duty value Dtyv in the step S451 orstep S452, in a final step S453, the controller 41 performs an operationcheck on the variable nozzle 53 using the subroutine of FIG. 96 based onthe command duty value Dtyv.

Referring to FIG. 96, in a step S481, the controller 41 first reads thecommand duty value Dtyv, engine rotation speed Ne, target fuel injectionamount Qsol and the cooling water temperature Tw.

In subsequent steps S482-S485, it is determined whether or not operationcheck conditions are satisfied. An operation check is performed onlywhen all these conditions are satisfied.

In the step S482, it is determined whether or not the target fuelinjection amount Qsol is less than a predetermined value QSOLDIZ#. Whenthis condition is satisfied, it means that the diesel engine 1 isperforming fuel cut.

In the step S483, it is determined whether or not the engine rotationspeed Ne is less than a predetermined value NEDIZ#. When this conditionis satisfied, it means that the rotation speed Ne of the diesel engine 1is in an intermediate or low speed region.

In the step S484, it is determined whether or not the cooling watertemperature Tw is less than a predetermined value TWDIZ#. When thiscondition is satisfied, it means that warming up of the diesel engine 1is not complete.

In the step S485, it is determined whether or not an operation checkflag Fdiz is zero. When this condition is satisfied, it means that anoperation check has not yet been performed.

When all the conditions are satisfied, an operation check counter valueCtFdiz is incremented in a step S486, and the routine proceeds to a stepS487.

If any of the determination results of the steps S482-S484 is notsatisfied, the subroutine resets the operation check flag Fdiz to zeroin a step S493, and proceeds to a step S494. However, when the operationcheck flag fdiz is one in the step S485, it proceeds to the step S494immediately.

In a step S487, the operation check counter value CtFdiz is comparedwith a predetermined upper limiting value CTRDIZH#.

When the operation check counter value CtFdiz is smaller than the upperlimiting value CTRDIZH#, in a step S488, the operation check countervalue CtFdiz is compared with a predetermined lower limiting valueCTRDIZL#. When the operation check counter value CtFdiz is not less thanthe lower limiting value CTRDIZL#, in a step S489, a duty value Dtyvntis set for checking operation using a subroutine shown in FIG. 97.

The upper limiting value CTRDIZH# is set to, for example, seven seconds,and the lower limiting value CTRDIZL# is set to, for example, twoseconds. In this case, the duty value for checking operation is set onlyin a five second interval of the difference between the upper limitingvalue and lower limiting value.

Here, referring to FIG. 97, a subroutine for setting the duty value foroperation check will be described.

The controller 41, in a step S501, first reads the operation checkcounter value CtFdiz and engine rotation speed Ne.

In a following step S502, a control pattern value Duty_pu is set bylooking up a map shown in FIG. 98 based on the difference of theoperation check counter value CtFdiz and lower limiting value CTRDIZL#.This map is previously stored in the memory of the controller 41 Thecontrol pattern value Duty_pu is set so that it repeatedly variesbetween zero and one with a short period according to the elapsed timeafter the operation check counter value CtFdiz exceeds the lowerlimiting value CTRDIZL#.

In a next step S503, a duty value Duty_p_ne commanded to the pressurecontrol valve 56 is calculated by looking up a map shown in FIG. 99previously stored in the memory of the controller 41, based on theengine rotation speed Ne. The duty value Duty_p_ne is set supposing thatthe duty for checking the opening and closing operation of the variablenozzle 53 differs according to the engine rotation speed Ne. Forexample, when the variable nozzle 53 is to be closed, it must closeagainst the exhaust gas pressure. The exhaust gas pressure increases inaccordance with the increase in engine rotation speed Ne.

Further, when the engine rotation speed Ne is in the high-speed region,the closing of the variable nozzle 53 to check operation has a majorimpact on the engine running environment. Therefore, in the high speedregion, the duty value Duty₁₃ p_ne is decreased as the engine rotationspeed Ne increases so as to reduce the impact on the engine runningenvironment.

In a following step S504, the duty value Dtyvnt is calculated bymultiplying the duty value Duty_p_ne by the control pattern valueDuty_pu, and the subroutine is terminated.

In this way, by terminating the subroutine of FIG. 97, the processing ofthe step S489 of FIG. 96 is terminated and the subroutine of FIG. 96 isalso terminated.

On the other hand, in the step S487 of FIG. 96, when the operation checkcounter value CtFdiz is not less than the upper limiting value CTRDIZH#,the processing of the step S490 is performed. Here, an immediatelypreceding value CtFdiz_(n−1) of the operation check counter value CtFdizoperation is compared with the upper limiting value CTRDIZH#. If theimmediately preceding valueCtFdiz_(n−1 is less than the upper limiting value CTRDIZH#, it means that CTRDIZH# reached the upper limiting value CTRDIZH# for the first time in the repeat execution of this subroutine, the duty value Dtyvnt is set to zero in a step S491, the operation check flag fdiz is set to one in a step S492, and the subroutine is terminated.)

By once setting the duty value Dtyvnt to zero in the step S491 when theoperation check is completed, the variable nozzle 53 fully opens. Thisoperation aims to maintain control precision during ordinary controlperformed thereafter. By setting the operation check flag fdiz to one,the determination result of the step S485 will always be affirmative inthe execution of the subroutine thereafter. It means the operation checkof the variable nozzle 53 is performed only once after starting thediesel engine 1.

On the other hand, when the immediately preceding value Ctfdiz_(n−1) ofthe operation check counter value Ctfdiz is not less than the upperlimiting value CTRDIZH# in the step S490, the subroutine proceeds to thestep S494. In the step S494, the operation check counter value Ctfdiz isreset to zero, and the routine proceeds to a step S495.

When the operation check counter value Ctfdiz is less than thepredetermined lower limiting value CTRDIZL# in the step S488, thesubroutine also proceeds to the step S495.

In the step S495, the duty value Dtyvnt for operation check is set equalto the command duty value Dtyv determined in the step S451 or step S452of FIG. 84, and the subroutine is terminated. In this case therefore,the ordinary control of the variable nozzle 53 is performed.

In particular, when operation of the pressure actuator 54 is unstablesuch as at low temperatures etc., this operation check of the variablenozzle 53 makes the operation of the variable nozzle 53 smooth andincreases reliability in control of supercharging pressure.

In this way, by ending the subroutine of FIG. 96, the processing of thesubroutine of FIG. 84 is terminated and the routine of FIG. 38 is alsoterminated.

Next, the effect of the supercharging pressure control of theturbocharger 50 according to this invention during acceleration of thediesel engine 1 will be described referring to FIGS. 104A-104E and FIGS.105A-105E.

FIGS. 104A-104E show an acceleration operation in the small exhaust gasamount region wherein the charging efficiency increases with increase inthe exhaust gas amount. This situation corresponds to the case shown bythe arrow A of FIG. 100.

The controller 41 separates the response delay of the intake fresh airamount relative to the command signal input into the pressure actuator54, into a gas flow lag and the response delay of the pressure actuator54 itself, and performs advance processing separately on each responsedelay. Due to the stepwise increase of the target fuel injection amountQsol and target intake fresh air amount tQac accompanying accelerationshown in FIGS. 104A, 104B, the target opening rate Rvnt of theadjustable nozzle 53 also decreases stepwise at a time t1, as shown inFIG. 104C.

In this case, the open loop control amount Avnt_f of the target openingrate wherein advance processing which compensates the gas flow lagrelative to the target opening rate Rvnt, first decreases in stepwisefashion as shown in FIG. 104C at the time t1, becomes smaller than Rvnt,and then gradually approaches the target opening rate Rvnt.

A value obtained by performing advance processing on the open loopcontrol amount Avnt_f for correcting the response delay of the pressureactuator 54, varies in stepwise fashion to a still smaller value thanthe open loop control amount Avnt_f at the time t1, as shown in FIG.104D, follows the open loop control amount Avnt_f, and then slowlyapproaches the target opening rate Rvnt.

Thus, according to this invention, separate advance corrections areperformed on two response delays having different characteristics, i.e.,the gas flow lag and the response delay of the pressure actuator 54, andthe two kinds of response delays are corrected with high precision.Hence, the cylinder intake fresh air amount Qac relative to the commandsignal input into the pressure control valve 56 increases withsufficient response, as shown by the solid line in FIG. 104E. In otherwords, the precision of advance processing in the control of the openingof the variable nozzle 53 improves. The dotted line of FIG. 104E showsthe variation of the cylinder intake fresh air amount Qac when noadvance processing is added to the target opening rate Rvnt.

In this control device, as the advance correction gain TGKVNTC when thepressure actuator 54 is driven in the increasing direction ofsupercharging pressure is set larger than the advance gain TGKVNTO whenthe pressure actuator 54 is driven in the decreasing direction ofsupercharging pressure in the small exhaust gas amount region, thesupercharging pressure can be started with sufficient response relativeto the command signal even when the gas flow lag increases due toincrease of the ÷pressure.

Also, regarding the time constant equivalent value Tcvnt, the value whenthe pressure actuator 54 is driven in the increasing direction ofsupercharging pressure is set smaller than the value when the pressureactuator 54 is driven in the decreasing direction of superchargingpressure.

The time constant equivalent value Tcvnt corresponds to the inverse ofthe time constant. When the pressure actuator 54 is driven in theincreasing direction of the supercharging pressure that is known tocause a gas flow lag of large time constant, the supercharging pressurecan be increased with good response due to this setting of Tcvnt.

FIGS. 105A-105E show an acceleration operation in the large exhaust gasamount region wherein the charging efficiency falls with increase in theexhaust gas amount.

This corresponds to the case shown by the arrow B of FIG. 100.

Also in this case, the target fuel injection amount Qsol and the targetintake fresh air amount tQac increase stepwise due to acceleration, asshown in FIGS. 105A and 105B. However, conversely to the small exhaustgas amount region, the target opening rate Rvnt of the variable nozzle53 increases stepwise at a time t2 in the opening direction of thevariable nozzle 53. Under this condition, as described hereabove, theadvance correction gain is a positive value less than 1.0, and equation(29) effectively functions as a delay processing equation.

Although the open loop control amount Avnt_f of the opening rate of thevariable nozzle 53 increases at the time t2 when the target opening rateRvnt increases stepwise, the increase amount is less than Rvnt.Subsequently, the open loop control amount Avnt_f gradually approachesthe target opening rate Rvnt, as shown in FIGS. 105C and 105fD.

In the large exhaust gas amount region also, as well as in the smallexhaust gas amount region, advance processing is performed to correctthe response delay of the pressure actuator 54 relative to the open loopcontrol amount Avnt_f.

The value after this advance processing is larger than the open loopcontrol amount Avnt_f as shown by the solid line of FIG. 105D, but thisadvance processed value will never be larger than the target openingrate Rvnt. In other words, the delay processing due to equation (29) inthis situation has a larger effect on the command signal than theadvance processing corresponding to the response delay of the pressureactuator 54. Due to this delay processing, the adjustable nozzle 53opens gradually. The gradual opening of this variable nozzle 53 has theeffect of preventing a temporary decline of the rotation speed of theexhaust gas turbine 52.

As the rotation speed of the exhaust gas turbine 52 does not fall, thecylinder intake fresh air amount Qac increases without delay. The dottedline of FIG. 105E shows the variation of the cylinder intake fresh airamount Qac when advance processing related to the response delay of thepressure actuator 54 is performed, but actual delay processing byequation (29) related to the gas flow lag is not performed.

Although it is also possible to determine the large exhaust gas amountregion, small exhaust gas amount region and intermediate region based onthe charging efficiency of the turbocharger 50 as described hereabove,the calculation of charging efficiency is complex.

By classifying the regions using the exhaust gas amount as parameterinstead of the charging efficiency as in this embodiment, classificationof the regions is easy and the composition of the program of thecontroller 41 may be simplified.

Next, a second embodiment of this invention relating to a subroutine forcalculating the target opening rate Rvnt will be described referring toFIGS. 56-58.

According to this embodiment, the target opening rate Rvnt is calculatedusing a subroutine shown in FIG. 56 instead of the subroutine of FIG.51.

In the subroutine of FIG. 56, the target EGR rate Megr is used forcalculating the target opening rate basic value Rvnt0 instead of the EGRamount equivalent value Qes0 used in the subroutine of FIG. 51. As aresult, in this subroutine, the step S303 which calculates the EGRamount equivalent value Qes0 in the subroutine of FIG. 51 is omitted.

Further, in the step S307, the target opening rate basic value Rvnt0 iscalculated from the set intake fresh air amount equivalent value tQas0and target EGR rate Megr using the map of FIG. 57 instead of the map ofFIG. 52. Likewise, in the step S308, the target opening rate basic valueRvnt0 is calculated from the set intake fresh air amount equivalentvalue tQas0 and target EGR rate Megr using the map of FIG. 58 instead ofthe map of FIG. 53.

The remaining features of the process are identical to those of thesubroutine of FIG. 51.

In the maps of FIG. 57 and FIG. 58, the target opening rate basic valueRvnt0 may be set based on the target intake fresh air amount tQac andreal EGR rate Megrd instead of setting it based on the set intake freshair amount equivalent value tQas0 and target EGR rate Megr. Further, thetarget opening rate basic value Rvnt0 may be set based on the targetintake fresh air amount tQac and target EGR rate Megr.

In the transient running state of the diesel engine 1, a delay occursuntil the real EGR rate Megrd catches up with the target EGR rate Megr,and due to the deviation from the EGR amount corresponding to the delay,an error occurs in the target opening rate basic value Rvnt0. When thetarget opening rate basic value Rvnt0 is set by using the real EGRamount Megrd, which is a value obtained by applying delay processing tothe target EGR rate Megr, the optimum target intake fresh air amount isobtained for all preselected characteristics including fuel consumption,exhaust gas composition and acceleration performance even in thetransient running state of the diesel engine 1. Further, simplerconformity and simplification of control logic can be achieved.

Next, a third embodiment of this invention will be described referringto FIGS. 106-108.

In this embodiment, the subroutine of FIG. 106 is used instead of thesubroutine for calculating the EGR valve opening surface area Aev ofFIG. 37 used in the first and second embodiment. The remaining featuresare identical to those of the first and second embodiments.

In the first and second embodiments, the EGR valve opening surface areaAev is calculated from the EGR flowrate Cqe and target EGR amount Tqek,but according to this embodiment, the real opening rate Rvnte of thevariable nozzle 53 is adopted as an approximation of the differentialpressure of the EGR valve 6.

The opening surface area Aev of the EGR valve 6 is calculated using thereal opening rate Rvnte and target EGR amount Tqec or real EGR rateMegrd as parameters.

First, in a step S511, the controller 41 reads the target EGR amountTqec per cylinder at the position of the EGR valve 6, a flowratelearning correction coefficient Kqac, an EGR flowrate feedbackcorrection coefficient Kqac0 and an EGR amount feedback correctioncoefficient Kqac00. These are values calculated by the routines of FIG.6 and FIG. 22.

In a following step S512, a target EGR amount Tqek2 is found per unitexhaust gas amount by the following equation (41). $\begin{matrix}{{Tqek2} = \frac{\frac{Tqec}{{Kqac} \cdot {Kqac0} \cdot {Kqac00}}}{{SVOL}\quad \#}} & (41)\end{matrix}$

where,

SVOL#=exhaust gas amount per cylinder.

In a step S513, the delay processing value Rvnte of the target openingrate Rvnt calculated by the routine of FIG. 60 is read.

In a next step S514, a target EGR valve opening surface area Eaevperunit exhaust gas amount is found referring to a map shown in FIG. 107which is prestored in the controller 41, based on the delay processingvalue Rvnte and target EGR amount Tqek per cylinder of the diesel engine1.

In the map of FIG. 107, the delay processing value Rvnte which is thehorizontal axis, may be considered to be approximately equal to thedifferential pressure upstream and downstream of the EGR valve 6. Forexample, providing that the opening of the EGR valve 6 is set constant,the smaller the delay processing value Rvnte, the larger the opening ofthe variable nozzle 53 and the higher the supercharging pressure.Consequently, the differential pressure upstream and downstream of theEGR valve 6 becomes large. Conversely,the larger the delay processingvalue Rvnte, the larger the opening of the variable nozzle 53 and thelower the supercharging pressure. Consequently, the differentialpressure upstream and downstream of the EGR valve 6 decreases.

Thus, the delay processing value Rvnte which is the horizontal axis maybe considered to represent the differential pressure upstream anddownstream of the EGR valve 6. By taking the EGR amount as the verticalaxis, the opening of the EGR valve 6 can be specified with theseparameters as can be understood from the map of FIG. 107. The figures inFIG. 107 are temporary value assigned to show the relative magnitude ofthe opening of the EGR valve 6.

The inventors obtained the map of FIG. 107 by experiment, but the EGRvalve opening area Aev may also be determined using a theoreticallydefined map as shown in FIG. 108.

In FIG. 107 and FIG. 108, the characteristics largely differ in theregion of the right-hand side of the map, but as control is not actuallyperformed in this region, there is no effect on the control whichevermap is used.

What is read from these maps is not the opening area of the EGR valve 6,but the target EGR valve opening area EAev per unit exhaust gas amount.This is in order to be able to apply the map without depending on theexhaust gas amount of the diesel engine 1.

After the controller 41 calculates the target EGR valve opening areaEAev per unit exhaust gas amount in the step S514, the target EGR valveopening area Aev is calculated by multiplying EAev by the exhaust gasamount per cylinder SVOL# of the diesel engine 1 in a step S515, and thesubroutine of FIG. 106 is terminated.

Thus, by taking the real opening rate Rvnte as an approximation of theupstream/downstream differential pressure of the EGR valve 6, it ispossible to calculate the target EGR valve opening surface area Aevdirectly without calculating the EGR flowrate Cqe. Therefore, the EGRcontrol logic can be simplified according to this embodiment, and thecontrol precision of the EGR valve also improves.

In the above embodiments, when the advance correction gains TGKVNTO,TGKVNTC used for calculation of the open loop control amount Avnt_f ofthe variable nozzle 53 are set, the charging efficiency is classifiedusing the exhaust gas amount as a parameter. As the intake air amountincreases assuming that the exhaust gas amount increases, it is alsopossible to classify charging efficiency by using the intake air amountas a parameter, and to apply the intake air amount instead of theexhaust gas amount to the horizontal axis of the map of FIG. 62 and FIG.63. Specifically, it is classified into a small intake air amount regionwhere the charging efficiency increases with increase of intake airamount, a large intake air amount region where the charging efficiencydecreases with increase of intake air amount, and an intermediate regionsituated therebetween.

In the above embodiments, the variable nozzle 53 is driven by thepressure actuator 54, but it is also possible to use other types ofactuator. In all the embodiments, the target opening rate Rvnt is usedas an operation target value of the variable nozzle 53, but it is alsopossible to use a target opening surface area.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the above teachings.

For example, the fresh air amount and supercharging pressure correspondwith each other, so the target supercharging pressure may also be usedinstead of the target intake fresh air amount tQac.

The turbocharger to which this invention is applied is not limited to aturbocharger comprising the variable nozzle 53. This invention may alsobe applied to all variable geometric turbochargers which permitvariation of the geometry of the exhaust gas turbine, such as aturbocharger comprising a scroll or diffuser which modifies the exhaustgas passage cross-sectional surface area of the exhaust gas turbine ofthe turbocharger.

This invention may be applied also to a diesel engine which does notperform exhaust gas recirculation. The diesel engine 1 is not limited toa “low-temperature premixing combustion type” in which the heatgeneration is produced by a single stage combustion. Thus, the inventionmay be applied also to an ordinary diesel engine in which diffusioncombustion is performed after premixing combustion.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

Industrial Field of Application

As mentioned above, this invention compensates the delay in thevariation of the intake air amount of a diesel engine due to operationof an actuator of a turbocharger according to the type of delay.Therefore, the response in an acceleration operation of a vehicle fittedwith the supercharged diesel engine, is enhanced.

What is claimed is:
 1. A control device for a turbocharger of an engine,the turbocharger comprising an actuator which adjusts an intake airamount of the engine according to a command signal, the control devicecomprising: a sensor which detects a running state of the engine; and acontroller functioning to: set a target intake air amount of the enginebased on the running state; calculate an operational target value of theactuator based on the target intake air amount; calculate a firstcompensation value of a response delay from operation of the actuator tovariation of the intake air amount; calculate a second compensationvalue of an operating delay of the actuator with respect to an input ofthe command signal to the actuator; calculate the command signal byperforming a processing based on the first compensation value and thesecond compensation value on the operational target value; and outputthe command signal to the actuator.
 2. The control device as defined inclaim 1, wherein the controller is further functioning to performprocessing on the operation target value based on the secondcompensation value after performing processing based on the firstcompensation value.
 3. The control device as defined in claim 1, whereinthe control device further comprises a sensor which detects an exhaustgas amount of the engine, and the controller is further functioning tocalculate the first compensation value by applying advance processing tothe operational target value when the exhaust gas amount of the engineis less than a predetermined amount.
 4. The control device as defined inclaim 1, wherein the control device further comprises a sensor whichdetects an exhaust gas amount of the engine, and the controller isfurther functioning to calculate the first compensation value byapplying delay processing to the operational target value when theexhaust gas amount of the engine is larger than a predetermined amount.5. The control device as defined in claim 1, wherein the control devicefurther comprises a sensor which detects an exhaust gas amount of theengine, the first compensation value includes an advance correctiongain, and the controller is further functioning to set the advancecorrection gain based on the exhaust gas amount of the engine.
 6. Thecontrol device as defined in claim 5, wherein the controller is furtherfunctioning to set the advance correction gain to a positive value lessthan one when the exhaust gas amount of the engine is greater than apredetermined amount.
 7. The control device as defined in claim 5,wherein the controller is further functioning to set the advancecorrection gain when the actuator is operating in an increasingdirection of the intake air amount, larger than the advance correctiongain when the actuator is operating in a decreasing direction of theintake air amount.
 8. The control device as defined in claim 1, whereinthe control device further comprises a sensor which detects an exhaustgas amount of the engine, the first compensation value includes a timeconstant equivalent value corresponding to the inverse of a timeconstant of the advance correction, and the controller is furtherfunctioning to determine the time constant equivalent value according tothe exhaust gas amount of the engine.
 9. The control device as definedin claim 8, wherein the controller is further functioning to set thetime constant equivalent value when the actuator is operating in anincreasing direction of the intake air amount, smaller than the timeconstant equivalent value when the actuator is operating in a decreasingdirection of the intake air amount.
 10. The control device as defined inclaim 1, wherein the second compensation value includes an advancecorrection gain related to a response of the actuator and the controlleris further functioning to set the advance correction gain when theactuator is operating in an increasing direction of the intake airamount, larger than the advance correction gain when the actuator isdriven in a decreasing direction of the intake air amount.
 11. thecontrol device as defined in claim 1, wherein the second compensationvalue includes a time constant equivalent value corresponding to aninverse of a time constant which represents an operation speed of theactuator, and the controller is further functioning to set the timeconstant equivalent value when the actuator is driven in an increasingdirection of the intake air amount, larger than the time constantequivalent value when the actuator is driven in a decreasing directionof the intake air amount.
 12. The control device as defined in claim 1,wherein the engine comprises an exhaust gas recirculation device whichrecirculates part of an exhaust gas into an intake fresh air of theengine, and the controller is further functioning to calculate a targetexhaust gas recirculation amount of the exhaust gas recirculation devicebased on the running state, calculate a first processing value based onthe first compensation value, calculate a control target value of theexhaust gas recirculation device based on the operating target valueprocessing value and target exhaust circulation amount, and control theexhaust gas recirculation device based on the control target value. 13.A control device for a turbocharger of an engine, the turbochargercomprising an actuator which adjusts an intake air amount of the engineaccording to a command signal, the control device comprising: means fordetecting a running state of the engine; means for setting a targetintake air amount of the engine based on the running state; means forcalculating an operational target value of the actuator based on thetarget intake air amount; means for calculating a first compensationvalue of a response delay from operation of the actuator to variation ofthe intake air amount; means for calculating a second compensation valueof an operating delay of the actuator with respect to an input of thecommand signal to the actuator; means for calculating the command signalby performing a processing based on the first compensation value and thesecond compensation value on the operational target value; and means foroutputting the command signal to the actuator.
 14. A control method of aturbocharger of an engine, the turbocharger comprising an actuator whichadjusts an intake air amount of the engine according to a commandsignal, the control method comprising: detecting a running state of theengine; setting a target intake air amount of the engine based on therunning state; calculating an operational target value of the actuatorbased on the target intake air amount; calculating a first compensationvalue of a response delay from operation of the actuator to variation ofthe intake air amount; calculating a second compensation value of anoperating delay of the actuator with respect to an input of the commandsignal to the actuator; calculating the command signal by performing aprocessing based on the first compensation value and the secondcompensation value on the operational target value; and outputting thecommand signal to the actuator.